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GCSE Chemistry 2 > Rates of Reaction - Topic 7 > Flashcards

Rates of Reaction - Topic 7 Flashcards

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1
Q

In a chemical reaction what do the reactants get converted into?

A

reactants ———> products

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2
Q

What are two general ways of measuring the rate of reaction?

A
  • rate at which the reactants are used up
  • rate at which the products are formed
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3
Q

General equation for calculation the rate (or speed) of reaction:

A

rate of reaction = change in amount of a reactant or product / time

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4
Q

Practical Examples of measuring how quickly products are made to calculate the rate of reaction:

A

This involves repeating the same reaction several times, each time changing one variable e.g. surface area. Examples:

  • Experiment in which cross disappears; you cannot see the cross anymore because solid sulfur (= precipitate) has been formed which makes the solution cloudy;
  • Time how long it takes to produce a certain amount of gas e.g. 40 ml of oxygen when hydrogen peroxide breaks down or decomposes into water and oxygen or when COis produced when limestone and an acid react.
  • Measuring gas production is a common method and needs a closed system to collect the gas and a device that will allow the volume of the gas to be measured (e.g. gas syringe or measuring cylinder) as shown below
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5
Q

Practical Examples of measuring how quickly reactants are used up to calculate the rate of reaction:

A
  • Follow the decrease in mass as the gas escapes
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6
Q

What does the particle collision theory state (for a reaction to take place)?

A
  1. Particles must collide
  2. Particles must collide successfully; a successful collision is called a reactant collision
  3. These collisions must be of sufficient number, ie. collisions must be equal or greater than the Activation Energy if they are to lead. to a successful reaction
    - reaction rate = number of successful/reactive collisions / time
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7
Q

How are rates of chemical reactions sped up (collisions)?

A

Rates of chemical reactions are speeded up if the number of collisions greater than activation energy increases

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8
Q

Activation Energy:

A
  • The minimum amount of energy required for a reaction to take place
  • It is the minimum amount of energy with wich the particles need to collide with to make the collisions successful
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9
Q

What happens if particles do not reach the activation energy?

A

The particles may still collide, but they will simply just bounce of each other

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10
Q

Factors affecting the rate of reaction:

A
  • Concentration - of solutions
  • Temperature
  • Surface area - for reactants in the solid state
  • Catalyst - presence or absence
  • Pressure - for reactants in gas state
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11
Q

How does concentration affect the rate of reaction?

A
  • Increase in concentration of reactants
  • More particles of reactants in same volume
  • Increased frequency of collisions
  • More frequent successful collisions between reactant particles in same period of time
  • Increased rate of reaction
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12
Q

Example of how concentration can affect the rate of reaction:

A
  • e.g reaction between magnesium and hydrochloric acid
  • Magnesium + hydrochloric acid —> magnesium chloride + hydrogen
  • Mg (s) + 2HCl (aq) —> MgCl2 (aq) + Hs2(g)
  • by increasing the concentration of the Hal the number of H ions within a certain volume is increased
  • more particles in the same volume there
  • more frequent collisions
  • more frequent successful collisions in same period of time
  • increased rate of reaction
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13
Q

How does temperature affect the rate of reaction?

A
  • Increasing the temperature of a reaction increases the kinetic energy of the particles this means:
    • the particle move faster
    • increased frequency of collision between particles
    • more frequent successful collision in same period of time
    • increased rate of reaction
  • Increasing the temperature of a reaction increases the kinetic energy of the particles this means:
    • more particles have energy that is equal to or greater than the activation energy
    • larger proportion of collisions are successful
    • more successful collisions in same period of time
    • increased rate of reaction
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14
Q

Describe the particles in a reaction at a lower temperature:

A
  • lower temperature
  • particles have less kinetic energy
  • particles move slower
  • less frequent collisions
  • less frequent successful collisions in same period of time
  • decreased rate of reaction
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15
Q

Describe the particles in a reaction at a higher temperature:

A
  • higher temperature
  • particles have more kinetic energy
  • particles move faster
  • increased frequency of collisions
  • more frequent successful collision in same period of time
  • increased rate of reaction
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16
Q

How does surface are affect the rate of reaction (solid reactants)?

A
  • Reduced particle size means there is an increase in SA
  • Greater area of contact between the (solid) reactants
  • More contact between (solid) reactants (as larger number of particles can collide with each other due to the greater SA)
  • Increased frequency of collisions
  • Increased number of frequent successful collisions in same period of time
  • Increased rate of reaction
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17
Q

How does changing pressure have an effect on reactions that only involve liquids and solids?

A

Have little or no effect on reactions only involving liquids and solids as the particles in these states are already close together

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18
Q

How does the pressure (for gas reactants) affect the rate of reaction?

A
  • Increased pressure means there are more gas particles in smaller volume
  • Smaller distance between gas particles
  • Increased frequency of collisions between reactant particles
  • More frequent successful collisions in same period of time
  • Increased rate of reaction
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19
Q

Describe the rate of reaction in general throughout an experiment:

A
  • In any reaction the rate of reaction is always the highest at the start and always lowers as the reaction goes on
  • So any reaction always slows down as soon as it starts
  • The amount (or concentration) of reactants is always the highest at the start of the reaction and decreases as the reaction progresses
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20
Q

Catalyst:

A
  • A substance that speeds up the rate of reaction without altering the products of the reaction, being itself unchanged chemically and in mass at the end of the reaction
  • It does this by lowering the activation energy by providing a different pathway for the reaction that has a lower activation energy than the uncatalysed reaction
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21
Q

Why are catalysts important in industry?

A
  • They lower E needed to start a reaction (Saves money)
  • Make the reaction faster - enabling more product to be produced each second
  • They can be used over and over again since they’re not used up (although catalysts can be poisoned if their surface is coated with another chemical)
22
Q

How do you make solid catalysts more efficient?

A
  • Designed to have a large surface area - e.g. finely divided catalyst
  • e.g. catalysts in a catalytic converter in a car exhaust is coated over a honeycomb structure that gives it a surface area of a few football pitches
23
Q

Disadvantages of catalysts:

A
  • Often expensive to buy so the initial expenditure can be large
  • Catalysts can be poisoned by other substances - if this happens the catalyst has to be either cleaned (often impossible to do) or replaced
24
Q

Examples of catalysts:

A
  • Transition metals and transition metal compounds are often good catalysts
  • Platinum, palladium, and rhodium are catalysts that are used in converters in cars. The metals are spread over a ceramic honeycomb structure to increase their surface area
  • Iron is a catalyst in the Harbour process - a reaction in which nitrogen combines with hydrogen to make ammonia
  • Manganese (IV) oxide is a catalyst used in the decompositions of hydrogen peroxide
25
Q

What are enzymes?

A

biological catalysts

26
Q

What are enzymes used in the production of?

A

alcoholic drinks

27
Q

Units used for rates of reaction:

A
  • g/s
  • g/min
  • cm3/s
  • cm3/min
28
Q

Is the activation energy different for each experiment?

A

yes

29
Q

Law of entropy:

A

things tend towards chaos, endothermic reaction

30
Q

How does using a catalyst affect the rate of reaction?

A
  • use a catalyst
  • provides an alternate energy pathway for the reaction with a lower activation energy
  • higher proportion of collisions are successful as more collisions are above the activation energy
  • so there are more successful collisions in same period of time
  • increased rate of reaction
31
Q

How does the surface area affect rate of reaction - Assessed GCSE Practical: What is the word and symbol equation for the reaction between calcium carbonate (marble chips) and hydrochloric acid?

A
  • calcium carbonate + hydrochloric acid —> calcium chloride + carbon dioxide + water
  • CaCO3(s) + 2HCl(aq) —> caCl(aq) + CO2(g) + H2O(l)
32
Q

How does the surface area affect rate of reaction - Assessed GCSE Practical: State 2 methods in which you could measure the rate of this reaction:

A
  • Rate at which gas is produced (product)
  • Rate at which mass is lost (reactant)
33
Q

How does the surface area affect rate of reaction - Assessed GCSE Practical: What are two ways of measuring gas production?

A
  • Gas syringe
  • Measuring cylinder
34
Q

How does the surface area affect rate of reaction - Assessed GCSE Practical: The reaction between calcium carbonate (marble chips) and hydrochloric acid: How do you use a gas syringe to measure the amount of product produced in a reaction?

A
  • This can be done using a syringe or an upside down water filled measuring cylinder (water displacement)
  • The acid is added to the carbonate, the bung quickly replaced and the volume of gas produced recorded every 10s
35
Q

How do you use a measuring cylinder to measure the amount of product produced in a reaction?

A

Use a measuring cylinder instead of a gas syringe

36
Q

How does the surface area affect rate of reaction - Assessed GCSE Practical: The reaction between calcium carbonate (marble chips) and hydrochloric acid: How do you measure the mass lost in a reaction to work out the rate of reaction?

A
  • As CO2 is a relatively heavy gas we can use a mass loss method
  • A conical flask is placed on a balance
  • The acid and carbonate are mixed and a cotton wool plug is placed in the top of the conical flask (this allows CO2 to escape but prevents loss of mass due to acid spray)
  • Reading are taken every 10s as the mass drops due to the lost CO2
37
Q

How does the surface area affect rate of reaction - Assessed GCSE Practical: The reaction between calcium carbonate (marble chips) and hydrochloric acid: Method

A
  • Put 20cm of 1.5 mol/dm HCI in a conical flask
  • Set up the equipment in the diagram above, fill a 100cm³ measuring cylinder with water, invert it and clamp it in place in the trough
  • Measure out 2g of large marble chips on a balance. Add them to flask and replace the bung as quickly as possible
  • Read the measuring cylinder every 10 seconds and keep taking results until you get the same result three times, the volume of gas goes beyond the scale or 180 seconds (3 minutes) has gone
  • Repeat the experiment for medium sized marble chippings, small chippings and calcium carbonate powder
38
Q

How does the surface area affect rate of reaction - Assessed GCSE Practical: The reaction between calcium carbonate (marble chips) and hydrochloric acid: Which variable can be measured to find the rate of reaction?

A
  • Mass loss of system
  • Volume of CO2 produced
  • Increase in pH
  • Decrease in concentration of acid
39
Q

How does the surface area affect rate of reaction - Assessed GCSE Practical: The reaction between calcium carbonate (marble chips) and hydrochloric acid: Which reaction was the slowest? How can you tell from the graph?

A
  • Large marble chips
  • Least steep gradient
40
Q

How does the surface area affect rate of reaction - Assessed GCSE Practical: The reaction between calcium carbonate (marble chips) and hydrochloric acid: As the marble chips get smaller their surface area increases. What effect does surface area have on rate of reaction and why?

A
  • SA:V of the marble chips increase —> the rate of reaction increases
  • Reduced particle size means there is an increase in SA
  • Greater area of contact between the reactants
  • More contact between reactants (as larger number of particles can collide with each other due to the greater SA)
  • Increased frequency of collisions
  • Increased number of frequent successful collisions in same period of time
41
Q

How does the surface area affect rate of reaction - Assessed GCSE Practical: The reaction between calcium carbonate (marble chips) and hydrochloric acid: Why do flour mills and sugar factories have to be careful that there are no naked flames or sparks anywhere near any of the plant?

A
  • The SA in both of factories of the flour and sugar would be massive therefore very little energy would be needed for a reaction to take place - an explosion could happen
  • Larger the SA the faster the rate of reaction
42
Q

How temperature affects the rate reaction between hydrochloric acid and sodium thiosulphate? - Assessed GCSE Practical: What is the word and symbol equation for the reaction?

A
  • sodium thiosulphate + hydrochloric acid —> sodium chloride + sulphur dioxide + water
  • Na2S2O3 (s) +2HCl (aq)—> 2 NaCl (aq)+ SO2 (g) + S (s) + H2O (l)
43
Q

How temperature affects the rate reaction between hydrochloric acid and sodium thiosulphate? - Assessed GCSE Practical: What is sulphur?

A

a yellow solid and one of the products in the reaction

44
Q

How temperature affects the rate reaction between hydrochloric acid and sodium thiosulphate? - Assessed GCSE Practical: How can we monitor the rate of reaction/what variables can we measure for the rate of reaction?

A

Measure time it takes to produce enough sulphur to block view of a cross

45
Q

How temperature affects the rate reaction between hydrochloric acid and sodium thiosulphate? - Assessed GCSE Practical: Method

A
  • Use a 50cm³ measuring cylinder to measure out separately 10cm of sodium thiosulfate solution and 40cm³ of water.
  • Put these solutions intoa conical flask.
  • Use a thermometer to measure the termperature of the solution in the conical flask.
  • Record this temperature in the table.
  • Place the flask over a cross.
  • Use a 10cm³ measuring cylinder to measure out 5cm³ of HCI.
  • Add the acid to the thiosulfate and time how long it takes for the mixture to become so cloudy that the cross is no longer visible.
  • Record the time in seconds not minutes and seconds.
  • Repeat the experiment several times but each time use a Bunsen burner to heat the thiosulfate and water.
  • You should aim for temperatures around 30, 40, 50 and 60°C, but record the actual temperature of the experinment (e.g. 28°C, 43°C, 51°C, 59°C).
46
Q

How temperature affects the rate reaction between hydrochloric acid and sodium thiosulphate? - Assessed GCSE Practical: How do we calculate the rate of reaction?

A
  • Rate of reaction = 1000/s (in seconds)
  • In this equation 1,000 just represents the amount (mass) of sulphur made (we need the same amount of sulphur to block our view of the cross in each experiment, so call this 1000 to find the reaction rate
47
Q

How temperature affects the rate reaction between hydrochloric acid and sodium thiosulphate? - Assessed GCSE Practical: What effect does temperature have on rate of reaction and why?

A
  • the higher the temperature the faster the rate of reaction
  • particles at higher temperature so have more kinetic energy
  • particles move faster
  • increased frequency of collision between particles
  • more frequent successful collision in same period of time
  • increased rate of reaction
48
Q

Practical Examples of measuring how quickly products are made to calculate the rate of reaction:

A
  • Experiment in which cross disappears; you cannot see the cross anymore because solid sulfur (= precipitate) has been formed which makes the solution cloudy
  • Measure the volume of hydrogen produced every 30 seconds during the reaction
  • Time how long it takes to produce a certain amount of gas e.g. 40 ml of oxygen when hydrogen peroxide breaks down or decomposes into water and oxygen or when COis produced when limestone and an acid react.
  • Measuring gas production
    • Is a common method and needs a closed system to collect the gas and a device that will allow the volume of the gas to be measured (e.g. gas syringe or measuring cylinder) as shown below
49
Q

Practical examples of measuring how quickly reactants are used up to calculate the rate of reaction:

A
  • Time how long it takes for a piece of magnesium to disappear
  • Follow the decrease in mass as the gas escapes
50
Q

What does the temperature of a system tell us about the particles?

A

The temperature of a system tells us the average kinetic energy of the particles

51
Q

What is a rule of thumb for how the rate of reaction changes as the temperature increases?

A

as the temperature increases the rate of reaction increases (’a rule of thumb’ is that 10 degrees C doubles the rate of reaction)

GCSE Chemistry 2 (29 decks)

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