6. Chemical Reactions Flashcards
What do physical changes produce?
Physical changes (such as melting or evaporating) do not produce any new chemical substances
Are physical changes hard to reverse?
NO
-These changes are often easy to reverse and mixtures produced are usually relatively easy to separate
What do chemical changes produce?
In chemical reactions, new chemical products are formed that have very different properties to the reactants
Are chemical changes hard to reverse?
YES
- Most chemical reactions are impossible to reverse
What accompany chemical changes?
Energy changes also accompany chemical changes and energy can be given out (exothermic) or taken in (endothermic)
Are the majority of chemical reactions exothermic or endothermic?
The majority of chemical reactions are exothermic with only a small number being endothermic
What is the correlation between the rate of reaction and the concentration of a solution?
Increase in the concentration of a solution, the rate of reaction will increase
Why does an increase in concentration lead to an increase in the rate of reaction?
This is because there will be more reactant particles in a given volume, allowing more frequent and successful collisions per second, increasing the rate of reaction
What is the correlation between the rate of reaction and the surface area of a substance?
Increase in the surface area of the solid, the rate of reaction will increase
Why does an increase in surface area lead to an increase in the rate of reaction?
This is because more surface area particles will be exposed to the other reactant so there will be more frequent and successful collisions per second, increasing the rate of reaction
What is the correlation between the rate of reaction and temperature?
Increase in the temperature, the rate of reaction will increase
Why does an increase in temperature lead to an increase in the rate of reaction?
This is because the particles will have more kinetic energy than the required activation energy, therefore there will be more frequent and successful collisions per second, increasing the rate of reaction
What is the correlation between the rate of reaction and the use of a catalyst?
This shows that when a catalyst is used, the rate of reaction will increase
Why does the use of a catalyst lead to an increase in the rate of reaction?
Catalysts reduce the activation energy as they create alternative pathways requiring lower activation energy, allowing more successful and frequent collisions
When does explosive combustion occur?
Explosive combustion occurs when there are many fine particles in the air
In what industrial processes is there a high risk of explosive combustion and why?
Many industrial processes such as metal working, coal mining or flour milling produce very fine and tiny particles
These particles have a very large surface area and are combustible in air
Even a small spark may cause them to ignite and since the surface area is so large, the rate of reaction can be incredibly fast, hence they are explosive
Describe the graph for using different concentrations to see their effect on the rate of reaction
Compared to a reaction with a reactant at a low concentration, the graph line for the same reaction but at a higher concentration has a steeper gradient at the start and becomes horizontal sooner
Describe the graph for using different surface areas to see their effect on the rate of reaction
Compared to a reaction with lumps of reactant, the graph line for the same reaction but with powdered reactant has a steeper gradient at the start and becomes horizontal sooner
Describe the graph for using a catalyst to see their effect on the rate of reaction
The diagram shows that when a catalyst is used, the activation energy is reduced as it creates an alternative pathway requiring lower activation energy, allowing more successful and frequent collisions
Describe the graph for using different temperatures to see their effect on the rate of reaction
Compared to a reaction at a low temperature, the graph line for the same reaction but at a higher temperature has a steeper gradient at the start and becomes horizontal sooner
Look at 7.1.2 and the different practicals
indeed
What is the activation energy?
Particles need to have a minimum amount of energy to react when they collide
This is called the activation energy
Why is the rate of reaction slow at low temperatures?
At low temperatures only a small number of particles will have enough activation energy so the reaction will be slow
Why is the rate of reaction higher at higher temperatures? in terms of kinetic energy
At higher temperatures the particles have more kinetic energy so they move faster and with more energy
The collisions are thus more energetic and there is a greater number of particles with sufficient energy to react, so the rate of reaction increases
What does increasing the concentration do in relation to space and how does this increase the rate of reaction?
Increasing the concentration means there are more particles per cm3, so there is less space between the particles
Since there are more particles then it follows that there are more collisions, hence the rate of reaction increases
In what conditions do photochemical reactions occur?
These reactions occur only when light is present
What increases the rate of photochemical reactions?
The greater the intensity of ultraviolet light then the greater the rate of reaction
What is an example of a photochemical reaction? Give an equation
Photosynthesis
6CO2 + 6H2O —> C6H12O6 + 6O2
What do black and white photography film surfaces contain?
crystals of silver bromide
What happens to silver bromide when exposed to light? Give an equation?
When exposed to light they decompose to silver:
2AgBr → 2Ag + Br2
What is the difference in colour between AgBr and Ag
AgBr - colourless at low concentrations
Ag - appears grey black
What causes the different shades of black on a photography film?
Parts of the film appear black, grey or white depending on the exposure:
Stronger light = black or dark grey
Weaker light = light grey
Not exposed = white
What is photosynthesis?
This is the process in which plants produce food for reproduction and growth
What does photosynthesis require?
The process requires sunlight and chlorophyll
What is the catalyst for photosynthesis?
Chlorophyll is the green pigment in plants which absorbs sunlight and acts as the catalyst for photosynthesis
When do most reactions go to completion?
Some reactions go to completion, where the reactants are used up to form the product molecules and the reaction stops when all of the reactants are used up
What is the difference with reversible reactions compared to normal reactions?
In reversible reactions, the product molecules can themselves react with each other or decompose and form the reactant molecules again
In which direction does a reversible reaction occur?
It is said that the reaction can occur in both directions: the forward reaction (which forms the products) and the reverse direction (which forms the reactants)
What symbol is used to indicate a reversible reaction?
⇌
What is an example of a reversible reaction?
N2 + 3H2 ⇌ 2NH3
What are hydrated salts?
Hydrated salts are salts that contain water of crystallisation which affects their molecular shape and colour
What is water of crystallisation?
Water of crystallisation is the water that is stoichiometrically included in the structure of some salts during the crystallisation process
What is a common example of a hydrated salt?
A common example is copper(II) sulfate which crystallises forming the salt copper(II) sulfate pentahydrate, CuSO4.5H2O
How is water of crystallisation indicated?
Water of crystallisation is indicated with a dot written in between the salt molecule and the surrounding water molecules
What are anhydrous salts?
Anhydrous salts are those that have lost their water of crystallisation, usually by heating, in which the salt becomes dehydrated
Give the word equation for the dehydration of Hydrated Copper (II) Sulfate
Hydrated Copper (II) Sulfate ⇌ Anhydrous Copper (II) Sulfate + Water
What happens to anhydrous copper (II) sulfate crystals when they’re added to water?
When anhydrous copper (II) sulfate crystals are added to water they turn blue and heat is given off (exothermic); this reaction is reversible
What happens when (now hydrated) copper (II) sulfate crystals are heated in a test tube?
When Copper (II) Sulfate crystals are heated in a test tube, the blue crystals turn into a white powder and a clear, colourless liquid (water) collects at the top of the test tube
Give the chemical equation for the dehydration of Hydrated Copper (II) Sulfate
CuSO4.5H2O (s) ⇌ CuSO4 (s) + 5H2O (l)
Give the word equation for the dehydration of Hydrated Cobalt (II) chloride
Hydrated Cobalt (II) Chloride ⇌ Anhydrous Cobalt (II) Chloride + Water
Give the chemical equation for the dehydration of Hydrated Cobalt (II) Chloride
CoCl2.6H2O (s) ⇌ CoCl2 (s) + 6H2O (l)
What happens to anhydrous blue cobalt(II) chloride crystals when they are added to water?
When anhydrous blue cobalt(II) chloride crystals are added to water they turn pink and the reaction is reversible
What happens to the the cobalt(II) chloride crystals when they are heated in a test tube?
When the cobalt(II) chloride crystals are heated in a test tube, the pink crystals turn back to the blue colour again as the water of crystallisation is lost
Why are the pink crystals know as hydrated cobalt (II) chloride?
The form of cobalt(II) chloride in the crystals that are pink is known as hydrated cobalt (II) chloride because it contains water of crystallisation
What does it mean if a reversible reaction is in a state of equilibrium?
When during the course of reaction, the rate of the forward reaction equals the rate of the reverse reaction, then the overall reaction is said to be in a state of equilibrium
How do the molecules behave in a reaction at equilibrium?
It is dynamic eg the molecules on the left and right of the equation are changing into each other by chemical reactions constantly and at the same rate
How does the concentration of reactants and products change in a reaction at equilibrium?
The concentration of reactants and products remains CONSTANT (given there is no other change to the system such as temperature and pressure)
In what conditions does a reaction reach equilibrium?
It only occurs in a closed system so that none of the participating chemical species are able to leave the reaction vessel
What does equilibrium position mean?
Equilibrium position refers to the relationship between the concentration of reactants and products at the equilibrium state
What does it mean When the position of equilibrium shifts to the left?
When the position of equilibrium shifts to the left, it means the concentration of reactant increases
What does it mean When the position of equilibrium shifts to the right?
When the position of equilibrium shifts to right, this means the concentration of product increases
What is a catalyst’s effect on the position of the equilibrium?
The presence of a catalyst does not affect the position of equilibrium but it does increase the rate at which equilibrium is reached
Why does a catalyst increase the rate at which equilibrium is reached?
This is because the catalyst increases the rate of both the forward and backward reactions by the same amount (by providing an alternative pathway requiring lower activation energy)
As a result, the concentration of reactants and products is nevertheless the same at equilibrium as it would be without the catalyst
What is Le Chatelier’s Principle ?
Le Chatelier’s Principle states that when a change is made to the conditions of a system at equilibrium, the system automatically moves to oppose the change.
How is Le Chatelier’s Principle used?
The principle is used to predict changes to the position of equilibrium when there are changes in temperature, pressure or concentration.
What is the effect of an increase in temperature on the position of the equilibrium?
Equilibrium moves in the endothermic direction to reverse the change
What is the effect of a decrease in temperature on the position of the equilibrium?
Equilibrium moves in the exothermic direction to reverse the change
What is the effect of an increase in pressure on the position of the equilibrium?
Equilibrium shifts in the direction that produces the smaller number of gaseous molecules to decrease the pressure again
What is the effect of an decrease in pressure on the position of the equilibrium?
Equilibrium shifts in the direction that produces the larger number of molecules of gas to increase the pressure again
What is the effect of an increase in concentration (of the reactant) on the position of the equilibrium?
Equilibrium shifts to the right to reduce the effect of increase in the concentration of a reactant
What is the effect of an decrease in concentration (of the reactant) on the position of the equilibrium?
Equilibrium shifts to the left to reduce the effect of a decrease in reactant (or an increase in the concentration of product)
What connects oxidation and reduction?
Oxidation and reduction take place together at the same time in the same reaction
These are called redox reactions
What are 3 key things which define oxidation?
Oxygen is added to an element or a compound
An element, ion or compound loses electrons
The oxidation state of an element is increased
What are 3 key things which define reduction?
Oxygen is removed from an element or a compound
An element, ion or compound gains electrons
The oxidation state of an element is decreased
What is the oxidation state?
The oxidation state (also called oxidation number) is a number assigned to an atom or ion in a compound which indicates the degree of oxidation (or reduction)
What does the oxidation state help you do?
The oxidation state helps you to keep track of the movement of electrons in a redox process
How is the oxidation state shown?
It is written as a +/- sign followed by a number.
What does the oxidation number refer to?
Oxidation number refers to a single atom or ion only
What is the oxidation number of a compound?
The oxidation number of a compound is 0
What is the oxidation number of an element?
The oxidation number of an element is 0
What is the oxidation number of oxygen in a compound?
The oxidation number of oxygen in a compound is always -2 (except in peroxide R-O-O-R, where it is -1)
What are ionic equations and what do they show?
Ionic equations are used to show only the particles that actually take part in a reaction
These equations show only the ions that change their status during a chemical process, i.e: their bonding or physical state changes
What are the other ions present in a reaction which are not involved called?
The other ions present are not involved and are called spectator ions
practice redox reactions
:-)
What is an oxidising agent?
A substance that oxidises another substance, in so doing becoming itself reduced
What are examples of an oxidising agent?
Common examples include hydrogen peroxide, fluorine and chlorine
What is a reducing agent?
A substance that reduces another substance, in so doing becoming itself oxidised
What are examples of. a reducing agent?
Common examples include carbon and hydrogen
Why is the process of reduction very important in the chemical industry?
The process of reduction is very important in the chemical industry as a means of extracting metals from their ores
How can redox reactions be identified?
Redox reactions can be identified by the changes in the oxidation states when a reactant goes to a product
(or by colour changes)
What are two common examples of substances which can de identified as a redox reaction by their colour change?
Two common examples are acidified potassium manganate(VII), and potassium iodide
What is potassium manganate and when is it used?
Potassium manganate (VII), KMnO4, is an oxidising agent which is often used to test for the presence of reducing agents
What colour change is shown by potassium manganate when added to a reducing agent?
When acidified potassium manganate (VII) is added to a reducing agent its colour changes from pink-purple to colourless
What is potassium iodide and when is it used?
Potassium iodide, KI, is a reducing agent which is often used to test for the presence of oxidising agents
What colour change is shown by potassium iodide when added to an oxidising agent?
When added to an acidified solution of an oxidising agent such as aqueous chlorine or hydrogen peroxide, the solution turns a brown colour due to the formation of iodine
Avg. Rate of Reaction=
Amount of reactant used or amount of product formed / Time
4 factors that affect the Rate of Reaction
Temp.
SA
Conc. of solutions/ Pressure of gases
Presence of a catalyst
Collision Theory
An explanation of chemical reactions in terms of reacting particles colliding with sufficient energy for a reaction to take place.
Activation Energy
The minimum energy needed for a reaction to take place.
What 2 factors make a reaction more likely to occur?
> Increasing the frequency of particle’s collisions.
> Increasing the energy they contain when they collide.
What effect does a larger Surface Area have on the rate of reaction?
It does not result in collisions with more energy, but it does increase the frequency of collisions.
Increasing the surface area of an object…
…increases its rate of reaction.
How does raising the temperature affect the rate of reaction?
RoR increases.
Why does heating a substance increase its rate of reaction?
> When a substance is heated, energy is transferred to its particles.
This means that the particles move around faster, causing them, to collide more frequently.
This gives them more chances to react.
(THIS FACTOR IS LESS IMPORTANT THAN THE FACT THAT THE COLLISIONS CONTAIN MORE ENERGY)
How does heating a substance affect a particle’s energy?
> Because the particles are moving faster, they have more energy.
This results in a higher proportion of particles having greater energy than activation energy.
This effects the rate of reaction.
What is the consequence of increasing the concentration of reactants in a solution?
It increases the rate of reaction because there are more particles of the reactants, making the collisions more frequent.
What is not affected by an increase in the pressure or concentration of a substance?
The energy with which particles collide. It only affects the frequency of collisions.
What is the consequence of increasing the pressure of reacting gases?
Gas particles are squashed closer together, which increases the chance of collisions and reactions.
Catalyst
A substance that increases the rate of reaction.
When is Iron used as a catalyst?
Ammonia production
When is Platinum used as a catalyst?
Nitric acid production
What can we do to make catalysts as effective as possible?
Increase their SA
When Platinum and Palladium used as catalysts?
In Catalytic Converters inside car engines.
Positives of using catalysts.
> They don’t get used up- only a small amount is needed.
They’re good for the environment (don’t burn as many fossil fuels).
Often cheaper than paying for extra energy.
Negatives of using catalysts.
> Often expensive.
What can differ in comparing reactions?
Different rates
Give an example of a slow reaction
Rusting of iron
Give an example of a moderate speed reaction
A metal, like magnesium, reacting with an acid to produce a gentle stream of bubbles
Give an example of a fast reaction
An explosion
What four things do rates of reaction depend on?
Temperature - Concentration (or pressure for gases) - Catalyst - Size of particles (or surface area)
How can you increase the rate of a reaction?
Increase temperature - Increase concentration - Add a catalyst - Crush solid reactants into smaller pieces (bigger sa)
On a typical graph for rates of reaction, what line would show the quickest reaction?
The line that becomes flat in the least time
What does the lowest gradient show?
The lowest reaction
How can the speed of a reaction be observed?
By how quickly the reactants are used up or how quickly the products are formed (easier to measure products formed)
What are the three different ways of measuring the speed of a reaction?
Precipitation
Change in mass (usually a gas given off)
The volume of the gas given off
How do you know if it is a precipitate reaction?
The solution becomes cloudy
How would you measure the speed of a reaction by the forming of a precipitate?
Draw a cross on a piece of paper and put the conical glass with the solution directly above it
Observe the cross through the solution and time how long it takes for the cross to disappear (solution cloudy)
The quicker the cross disappears…
The quicker the reaction
What are the limitations of the precipitation method?
Initial solution has to be see through
- The results are very subjective
How can the change in mass be shown by the gas given off?
Using a mass balance, as the gas is released the mass disappearing is easily measured by the balance
The quicker the reading drops on the balance…
The faster the reaction
What are the advantages and disadvantages of using gas given off as a guide to the mass lost?
Advantage:
Results can be easily plotted on a rates of reaction graph
Very accurate as the mass balance is precise
Disadvantage:
- Releases gas straight into the room
How is the volume of a gas given off measured?
Using a gas syringe - the more gas given off during the reaction time interval, the faster the reaction
How do we know when the reaction has finished?
No more gas will be produced
What can be done with the results collected?
A graph of gas against time elapsed could be plotted to give a rate of reaction graph
Why are gas syringes very accurate?
They give volumes to the nearest millilitre
*however you need to be careful because if the reaction is too vigorous, you can blow the plunger out of the end of the syringe!
What does the reaction of hydrochloric acid and marble chips represent?
The effect of breaking the solid up into small bits
Describe an experiment using hydrochloric acid and marble chips
Measure the volume of gas evolved with a gas syringe and take readings at regular intervals - Make a table and plot the results on a graph - Repeat the experiment with exactly the same volume of acid but with the marble crunched up - Then repeat with the same mass of powdered marble instead of marble chips - Compare results
On the graph for hydrochloric acid and marble chips, what should x and y be?
The independent variable (x) = time The dependent variable (y) = volume
What can a graph conclude?
An increase in surface area (small chips) causes more frequent collisions, so the rate of the reaction is faster.
What does the reaction of magnesium metal with dilute HCL represent?
The effect of increases concontration (as is the marbe/acid reaction)
What does the reaction with magnesium metal and dilute HCL give off?
A hydrogen gas which can be measured with a mass balance.
What does the reaction with magnesium metal and dilute HCL give off?
A hydrogen gas which can be measured with a mass balance.
What are the independent and dependent varibles in the magnesium metal with dilute HCL?
Independant variable = Time
Dependant variable = Mass loss
What else can be used instead of a mass balance?
A gas syringe
What is the method for the magnesium metal and dilute HCL?
Take readings at regular intervals
Put the results in a table and work out the loss of mass for each reading
Plot a graph
Repeat with more concentrated acid solutions but the same amount of magnesium and volume of acid
How can we find the rate of reaction? (2)
Measure how quickly reactants are used up
Measure how quickly products are formed
What is the relationship between surface area and reaction rate? (2)
Rate of reaction increases when surface area is increased
Greater the surface area, more particles available to react, particles collide often
What is the danger of explosive reactions? (5)
Industrial processes cause fine powders to get into air
Powders are highly combustible
Burn readily in air due to high surface area
E.g. flour in flour mills/ wood dust in saw mills
Methane in coal mines can form explosive mixture with air
What is the relationship between catalysts and reaction rate? (3)
Catalyst can be used over and over again, not used up
Catalysts provides a more ideal environment as it lowers the activation energy
Often in pellets or wire gauzes - large surface for reactions to occur on
What is the relationship between concentration and reaction rate? (4)
increasing concentration of reactants increases rate of reaction
Concentrated solutions have more particles of solute per unit volume than dilute
Higher concentration → more frequent collision of particles
Rate of reaction depends on number of successful collisions per second, more collisions → faster
What is the first way temperature can affect reaction rate? (3)
Higher temperature → greater rate of reaction
Temperature increase, particles gain energy, move faster and collide more often
Increased rate
What is activation energy?
minimum amount of energy particles need in order to react
What is the second way temperature can affect reaction rate?
Temperature higher → more particles have minimum activation energy when colliding, higher chance of successful reactions
What are photochemical reactions?
chemical reactions started by ultraviolet or visible light.
What are hydrated salts?
Salts that have water as a part of their structure
What is water in crystallisation?
Water in the salt
What is anhydrous?
without water
What happens when crystals are heated?
water in crystallisation is lost?
What happens when you heat crystals of blue copper (II) sulfate?
they decompose to form a white powder
What is the word equation for the heating of hydrated copper (II) sulfate?
hydrated copper (II) sulfate => (heat) => anhydrous copper (II) sulfate (white + water
What is the symbol equation for the reversible heating of hydrated copper (II) sulfate?
CuSo4.5H2O (s) ⇌ (forward/backward) CuSo4 (s) + 5H2o (l)
What is the symbol equation for the reversible heating of hydrated copper (II) sulfate?
CuSo4.5H2O (s) <=> (forward/backward) CuSo4 (s) + 5H2o (l)
What is equilibrium?
Reactions in which both forward and reverse reactions are occurring
What are the features of equilibrium reaction?
Products/ Reactants must not escape, reaction in closed system
At equilibrium, reactants are continually being changed to products and products back to reactants (dynamic equilibrium)
At equilibrium concentration of reactants and products do not change (same as the start), as rate of forward reaction = rate of reverse reaction
Equilibrium can be approached from either direction
What is the position of equilibrium? (3)
Position of equilibrium tells how far reaction goes in favour of reactants or products/
Concentration of products greater => position of equilibrium to the right.
Concentration of reactants greater => position of equilibrium to the left.
When the concentration of reactant is increased, where does equilibrium move and why
equilibrium moves to the right, to form more products until equilibrium is restored - keeps relative concentrations of products and reactants the same as before
When the concentration of product is increased, where does equilibrium move?
equilibrium moves to the left to form more reactants
What reactions can pressure only affect?
reactions where there is a gas in the equation
If there are equal volumes or moles of gas on both sides of the equation, what is the effect of increasing pressure?
no effect
In (2SO2 + O2 => 2SO3), where does an increase in pressure do?
moves the reaction to the write , more SO2 and O2 combine to form SO3
If a reaction is exothermic in the forward direction, what will it be in the reverse reaction?
Endothermic
For an forward exothermic reaction, when temperature increases, where does equilibrium shift?
Equilibrium shifts in favor of the reverse reaction
For an forward endothermic reaction, when temperature increases, where does equilibrium shift?
Equilibrium moves to the right to favor products.
What do physical changes not produce?
New chemical substances
What is it easy to do with physical changes?
Easy to reverse
Give examples of physical changes.
Evaporating
Melting
What do chemical changes produce?
New chemical products that have very different properties to the reactants. These reactions are impossible to reverse.
What are most chemical reactions?
Exothermic
How can you increase the rate of reaction?
Increasing the temperature
Increasing the surface area
Increasing the concentration
Increasing the pressure
Adding a catalyst
How does increasing the temperature increase the rate of reaction?
Particles have more energy so hit each other more often and more of the collisions have enough energy to react
Increase in collision rate+ energy
How does increasing the surface area increase the rate of reaction?
There are more particles of the solid able to collide with particles of a liquid
How does increasing the concentration increase the rate of reaction?
The particles are closer together so are more likely to collide
Increases collision rate ONLY
How does increasing the pressure increase the rate of reaction?
The particles are closer together so are more likely to collide
How does adding a catalyst increase the rate of reaction?
A catalyst reduces the activation energy needed and particles need less energy to collide with each other
How can you measure the rate of reaction?
Measuring the rate at which reactants are used up
Measuring the rate at which products are made
Why do explosive combustions happen in wind mills?
There are fine particles in the air and these have a large SA and are combustible in air because the rate of reaction is fast
How can you investigate the rate of reaction? -3
Measuring the loss in mass when a gas is made
Measuring the volume of gas given off
Measuring the length of time for a precipitate to be made
What is a catalyst?
A substance that speeds up the rate of reaction without being used up
What is the activation energy?
The minimum energy needed to break bonds to start a chemical reaction
When do photochemical reactions occur?
When light is present
In photochemical reactions how can you speed up the rate of reaction?
Increasing the UV intensity
Give the equation for the substitution of H2 atoms in methane by chlorine
CH4 + Cl2 –> CH3Cl +HCl
What do black and white photography film surfaces contain?
Silver bromide crystals that decompose to silver when exposed
Give the equation for the decomposition of silver bromide crystals?
2AgBr –> 2Ag + Br2
What colour is AgBr in low concentration?
White/ light grey
What colour is AgBr in strong light?
Black/dark grey
What can happen in reversible reaction?
The product molecules can themselves react with each other or decompose and form reactant molecules again. It can occur in both directions
Give an example of a hydrated salt- chemical
CuSO4.5H20
What are anhydrous salts?
Those that have lost their eater of crystallization by heating
Give the chemical equation for the dehydration of copper (II) Sulphate
CuSO4.5H2O ⇌ CuSO4 + 5H20
Give the chemical equation for the dehydration of copper (II) Sulphate
CuSO4.5H2O (reversible reaction sign) CuSO4 + 5H20
What is the colour change for the dehydration of copper II sulphate
Blue to white
What happens when anhydrous copper sulphate crystals are added to water?
They turn blue and heat is given off
What happens when hydrous copper sulphate is heated?
Blue crystals turn white and a clear colourless liquid collects at the top
Give the equation for the dehydration of cobalt(II) Chloride
CoCl2. 6H2O ⇌ CoCl2 + 6H2O
When is equilibrium reached?
When the rate of forward reaction = rate of reverse reaction
What are characteristics of a reaction at equilibrium?
It is dynamic- molecules on the left and on the right of the equation are changing into each other
the concentration of reactant and products are constant
Occurs in a closed system so that none of the participating chemical species are able to leave the reaction
In the reaction between H2 and N2 in Haber process, What is happening at the beginning?
When only H2 and N2 are present at the beginning of the reaction the forward reaction is at its highest since conc of H2 and N2 are at their highest
In the reaction between H2 and N2 in Haber process, what happens after the beginning?
Conc of H2 and N2 decrease so the rate of forward reaction decreases and at the same time the conc of ammonia is increasing so the backward reaction increases
In the reaction between H2 and N2 in Haber process, what happens in the end?
Since no gases escape, equilibrium is reached
Give the equation for the Haber process
3H2 + N2 ⇌ 2NH3
What happens when the equilibrium position shifts to the left?
The concentration of reactants increase
What happens when the equilibrium position shifts to the right?
The concentration of product increases
What does the presence of a catalyst do? Why?
Does not affect the position of equilibrium but increases the rate at which equilibrium is reached. This is because the rate of both forward and backward reactions increase
What is Le Chatelier’s Principle?
When a change is made to the conditions of a system at equilibrium the system automatically moves to oppose the change
What happens when there is an increase in temperature?
Equilibrium moves in the endothermic direction to reverse the change
What happens when there is a decrease in temperature?
Equilibrium moves in the exothermic direction to reverse the change
What happens when there is an increase in pressure?
Equilibrium shifts in the direction that produces the smaller number of molecules of gas to decrease the pressure
What happens when there is a decrease in pressure?
Equilibrium shift in the direction that produces the larger number of molecules of gas to increase the pressure
What happens when there is an increase in concentration?
Equilibrium shifts to the RIGHT to reduce the effect of increase in concentration of reactant
What happens when there is a decrease in concentration?
Equilibrium shifts to the LEFT to reduce the effect of decrease in reactant
what is a catalyst
substance that increases the rate of reaction and is unchanged at the end of the reaction
what does a catalyst decrease?
the activation energy
Describe the effect on the rate of reaction of changing the concentration of solutions
Increasing the concentration of reactants in a solution generally leads to an increase in the rate of reaction. This is because a higher concentration of reactant molecules means that there are more molecules available to collide with each other, increasing the frequency of collisions and, therefore, the rate of reaction. This effect is known as an increase in the reaction rate due to an increase in the concentration of the reactants, or simply an increase in concentration.
Conversely, decreasing the concentration of reactants in a solution will generally lead to a decrease in the rate of reaction. This is because a lower concentration of reactant molecules means that there are fewer molecules available to collide with each other, reducing the frequency of collisions and, therefore, the rate of reaction. This effect is known as a decrease in the reaction rate due to a decrease in the concentration of the reactants, or simply a decrease in concentration.
Describe the effect on the rate of reaction of changing the pressure of gases
Increasing the pressure of a gas will generally lead to an increase in the rate of reaction. This is because an increase in pressure leads to a decrease in volume, causing the gas molecules to become more densely packed and increasing the frequency of collisions between them. As a result, the rate of reaction increases. This effect is known as an increase in the reaction rate due to an increase in pressure, or simply an increase in pressure.
Conversely, decreasing the pressure of a gas will generally lead to a decrease in the rate of reaction. This is because a decrease in pressure leads to an increase in volume, causing the gas molecules to become more spread out and decreasing the frequency of collisions between them. As a result, the rate of reaction decreases. This effect is known as a decrease in the reaction rate due to a decrease in pressure, or simply a decrease in pressure.
what does a catalyst decrease?
what does a catalyst decrease?
Define a redox reaction
a reaction involving simultaneous oxidation and reduction
Define oxidation
as gain of oxygen
define reduction
loss of oxygen
name the differences of reduction and oxidation in terms of electrons and oxidation numbers
oxidation= gain of electrons and an increase of oxidation num
reduction=loss of electrons and a decrease of oxidation num
Define an oxidising agent
a substance that oxidises another substance and is itself reduced
Define a reducing agent
a substance that reduces another substance and is itself oxidised
7 properties that affect the rate of a chemical reaction
Temperature
Concentration
Catalyst
Surface area
Pressure (gases)
pH
Light intensity
Gradient of a graph = ?
delta y / delta x
Describe an experiment to investigate the affect of varying temperature on the rate of a chemical reaction
Do the same for the affect of concerntration
CROSS DISAPPEARING EXPERIMENT
1-Measure a fixed volume of you solution e.g. 10cm^2 of Sodium thiosulphate (Na2S2O3) and fixed volume of water e.g. 40cm^3
2-Add 5cm^3 of HCL in the conical flask
3-Measure the initial temperature of the solution and start the stop watch
4-Record time for the cross to disappear
5-Repeat the experiment (without changing any of the measurements) at different temperatures
You can vary the temperature using a bunsen burner
For concentration you do the same thing but the temperature becomes constant and you vary the amount of water you add
Difference between a catalyst and a catalase
Catalases are enzymes where as catalysts are not
Equipment used to measure the amount of gas produced (2)
Either collected over water
- Gas syringe
Define dynamic equilibrium
The rate of the forward and backward reactions are equal
1-Equation for the Haber process
2-What type of reaction if the forward reaction? (Delta H)
3-What happens when you increase the pressure?
4-What happens when you increase the temperature?
1 - 3H2(g) + N2(g) 2NH3(g)
2 - Exothermic
3 - Moles of reactants : products is 4:2 so an increased pressure will favour products
4-Favours reactants as the forward reaction is exothermic
Describe an experiment that show cases a reversible reaction
HYDRATED COPPER (II) SULPHATE SOLID
1-Place one spatula of copper(II) sulphate powder into a boiling tube
2-Heat the boiling tube over a bunsen burner (blue flame)
3-Copper(II) sulphate is white when it is anhydrous (after heating it).
It will turn blue again if you add water to it
Conditions for Haber process (3)
Low temperature = 450 degrees C
High pressure = 200 atm
Iron (III) catalyst
1 - Raw materials of the Haber process (2)
2 - How do you obtain the raw materials?
1-Nitrogen and hydrogen
2-Nitrogen comes from the air and hydrogen is usually obtained through either cracking or reacting natural gases e.g. methane with steam
Uses of Ammonia (3)
Making medicines
Making fertilizers
Making explosives
What if the purpose of the Haber process?
To produce ammonia
General formula for an equilibrium reaction?
A + B C + D
Chemical equilibrium law?
Le Chantelier’s principle
When a reversible reaction is in equilibrium and you make a change, the system acts to oppose the change, and restore equilibrium. A new equilibrium mixture forms
Equilibrium
The point in a reversible reaction when the forwards and backwards rate of reaction are the same. Therefore, the amounts of substances present in the reacting mixture remain constant.
If the forward reaction produces more molecules of gas…
… an increase in pressure decreases the amount of products formed.
…. a decrease in pressure increases the amount of products formed.
If the forward reaction produces less molecules of gas…
… an increase in pressure increases the amount of products formed.
… a decrease in pressure decreases the amount of products formed.
When does changing the pressure affect a reaction’s equilibrium?
If there are different numbers of molecules of gases on either side of the equation.
If the forward reaction is exothermic…
… an increase in temperature decreases the amounts of product formed.
… a decrease in temperature increases the amount of products formed.
If the forward reaction is endothermic….
… an increase in temperature increases the amount of products formed.
… a decrease in temperature decreases the amount of products formed.
Materials needed to produce ammonia
> Nitrogen from the air
> Hydrogen mainly from natural gas.
Conditions needed for the Haber process.
> High temp (about 450 degrees)
High pressure (about 200 atmospheres)
An iron catalyst.
Haber process in 5 steps.
Gaseous nitrogen + hydrogen enter the machine.
The gases are compresses to 200 atom and heated to 450 degrees.
Passed over iron catalyst.
Emerging mixture is cooled and the ammonia liquefies, separating it from he unseated nitrogen/hydrogen.
Unreacted gases return to the beginning.
Use of ammonia
Fertilisers
Why is a pressure of 200 atmospheres used in the Haber process?
The forward reaction produces less molecules of gas, so to get the maximum yield of ammonia, the pressure has to be as high as possible. However, above 200 atmo, special reaction vessels and pipes have to be used so that there is no danger of explosion. Therefore, to keep the process economical, a compromise is made.
Why is a temperature of 450 degrees used for the Haber process?
Because the forward reaction is exothermic, using a low temperature would increase the yield. However, doing so would make the process very slow and not commercially viable. Using a low temperature could also reduce the effectiveness of the iron catalyst.
How does the use of a catalyst affect the Haber process?
It speeds up both the forwards and backwards reaction, but has no effect on the actual yield.
What are group 7 and group 1 elements called?
Group 7 = Halogens
Group 1 = Alkali metals
Reactivity trend in group 7 and group 1?
More reactive as you go down group 1
- More reactive as you go up in group 7
Steps of the contact process + all the equations
1 - Make sulphur dioxide gas. Roasting suphide ores or burning sulphur in air
S(l) + O2(g) —-> SO2(g)
2 - Make sulphur trioxide. React with more oxygen from the air. Add Vanadium five oxide (V2O5) as a catalyst
2SO2(g) + O2(g) 2SO3(g)
3 - Sulphur trioxide is dissolved in concerntrated sulphuric acid to make liquid Oleum
SO3(g) + H2SO4(l) —-> H2S2O7(l)
4 - Liquid oleum is diluted with measured amounts of water to create the correct concerntration of H2SO4
H2S2O7(l) + H2O(l) —-> 2H2SO4(l)
Uses of sulphur (4)
Cosmetics
Shampoos
Making pesticides
Added to rubber e.g. it’s added to car tyres to toughen them up. It’s called vulcanizing
Uses of sulphur dioxide (3)
Sterilizing agent e.g. dried fruit
Bleach for wool, silk and wood pulp to make paper
Prevents moulds
Disadvantage of sulphur dioxide
Why? (4)
ACID RAIN
Sulphur dioxide that escapes to the air reacts with the water droplets in clouds to form dilute sulphuric acid
Affects pH of water (kill fish) and affects species that are pH sensitive
Ruin infrastructure
Destroys habitats
Describe an experiment where you make a fertilizer
AMMONIUM SULPHATE FERTILIZER
1 - Put a measured amount of sulphuric acid into an evaporating basin
2-Add ammonia solution a little at a time, with stirring until a distinct smell of ammonia is obtained
3-Check the pH using indicator paper. Continue with step 2 until the pH showing up as 7
4-Evaporate the solution to about 1/5 of its original volume
5-Filter off the crystals and leave to dry
