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Chemistry IG > Topic 6 > Flashcards

Topic 6 Flashcards

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1
Q

What is needed for a chemical reaction to occur?

A
  • collide in the correct orientation
  • with enough activation energy (energy for a reaction to take place)
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2
Q

What is rate of reaction?

A

Speed at which the reaction takes place

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3
Q

How can rate of reaction be increased in relation to particles?

A
  • Increase frequency of particle collisions
  • Increase the kinetic energy of particles
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4
Q

What are the ways to increase rate of reaction?

A
  1. Reduce volume
  2. Increase temperature
  3. Increase surface area
  4. Using a chemical catalyst
  5. Increase concentration
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5
Q

How does changing concentration impact rate of reaction?

A

Increasing the concentration of a solutionwill increasethe rate of reaction. This is because there will be more reactant particles per unit volume, leading to more collisions per second and allowing more frequent and successful collisions per second, increasing the rate of reaction.

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6
Q

How does changing pressure change the rate of reaction?

A

For a gaseous reaction, increasing the pressure means the same number of particles will occupy a smaller volume. If you double the number of particles, you will double the number of collisions per second. The number of collisions isproportionalto the number of particles present

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7
Q

How does changing surface area change the rate of reaction?

A

Increasing the surface area of a solidwill increasethe rate of reaction. This is because moreparticles on the outside are exposed, increasing the frequency of collisions

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8
Q

How does changing temperature change the rate of reaction?

A

Increasing the temperature will increase 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 collisionsanda higher proportion of particles have energy greater than the activation energy, this causes more successful collisions per second, increasing the rate of reaction.

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9
Q

How does adding a catalyst change the rate of reaction?

A

The mass of a catalyst at the beginning and end of a reaction is thesameand they do not form part of the equation. Different processes require different types of catalysts, but they all work on the same principle of providing adifferent pathwayfor the reaction to occur that has alower activation energy. This means a higher proportion of the reactant particles have energy greater than the activation energy and will result in more successful collisions per second.

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10
Q

What are chemical catalysts?

A

Chemicals that speed up the rate of a reaction without being used up or changed in the process.

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11
Q

What are enzymes?

A

Proteins that act as biological catalysts. They work at a specific temperature and pH. At extreme conditions, enzymes become denatured and no longer function

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12
Q

During the process of a reaction what happens to the reactants and products?

A

Concentration of reactants decreases and concentration of products increases

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13
Q

Why does the concentration of reactants decrease as the reaction continues?

A

Because overtime the reactants are reacting to form the products over time, therefore the reactants decrease and products increase

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14
Q

What does the steepness of the reaction graph tell us?

A

How quickly the product was formed

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15
Q

Why does the reaction graph flatten out?

A

When the limiting reagent has been used up and reaction has stopped

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16
Q

Why does a reaction’s rate decrease over time?

A

A reaction’s rate decreases over time because the concentration of reactants decreases, reducing the frequency of successful collisions.
In a chemical reaction, reactants are transformed into products. As the reaction progresses, the concentration of the reactants decreases because they are being used up to form the products. This decrease in concentration reduces the number of successful collisions between reactant particles, which in turn slows down the rate of the reaction.

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17
Q

How can rate of reaction be measured?

A

By looking at the rate at which reactants are used up and the rate at which products are formed. Things that can be measured
- Mass of substance (using balance)
- Volume of gas (using gas syringe or inverted measuring cylinder)

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18
Q

What is breaking bonds?

A

Endothermic, requires/absorbs energy

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19
Q

What is bond forming?

A

Exothermic, releases energy

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20
Q

What is needed to make new products?

A

Bonds between reactant particles are broken and bonds are formed between product particles

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21
Q

What is endothermic?

A

Involves absorbing energy, temperature of surroundings decreases
Energy absorbed to break bonds > energy released to make bonds

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22
Q

What is exothermic?

A

Involves releasing energy, temperature of surroundings increases
Energy absorbed to break bonds < energy released to make bonds

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23
Q

What is enthalpy?

A

Change in energy between reactants and products and units are kJ/mol. The symbol is ΔH

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24
Q

What is the enthalpy of an exothermic reaction?

A

Negative
reactants > products

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25
Q

What is the enthalpy of an endothermic reaction?

A

Positive
products > reactants

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26
Q

What are the two axes of an enthalpy reaction graph?

A

vertical: energy
horizontal: direction of reaction

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27
Q

Formula to calculate enthalpy

A

ΔH = (total energy of bonds broken) - (total energy of bonds made)

28
Q

Steps to calculate enthalpy?

A
  1. Draw all covalent bonds in reactant and product molecule (If there’s two moles there is two molecules)
  2. Calculate total energy of bonds being broken
  3. Calculate total energy of bonds being made
  4. Calculate enthalpy
29
Q

What is a reversible reaction?

A

the product molecules can themselves react with each other or decompose and form the reactant molecules again. It is said that the reaction can occur inbothdirections: the forward reaction (which forms the products) and the reverse reaction (which forms the reactants)

30
Q

Symbol for reversible reaction?

A

⇌
Two half arrows

31
Q

How can some chemical reactions be reversed?

A

Adding water or heating to remove water by evaporation

32
Q

Colour change from hydrated copper sulfate to anhydrous copper sulfate

A

Blue -> white

33
Q

Colour change from hydrated cobalt chloride to anhydrous cobalt chloride

A

Pink -> blue

34
Q

What happens in more complex reversible reactions?

A

Reactants become products at the same time that products become reactants. These reactions usually don’t complete and the reaction mixture consists of both reactants and products

35
Q

Are there same number of reactants and products in equilibrium?

A

No, It just means that it’s at constant rate

36
Q

What are the two conditions for equilibrium?

A

A closed system (no loss of matter), no observable change, rate of forward and backward reaction is equal

36
Q

What is dynamic equilibrium?

A

When the rate of forward reaction is equal to the rate of backward reaction and there is no observable change

36
Q

What is Le Chatelier’s principle?

A

“When a change is made to a system at equilibrium, the system will oppose the change by minimising the effect of the change.”
To oppose the change either the forward or backward reaction will be favoured

37
Q

How can you change the direction of a reversible reaction?

A

Changing the reaction conditions (concentration, pressure, temperature) could alter the position of equilibrium

38
Q

What does it mean if the reaction moves to the right?

A

More products and it is a forward reaction

39
Q

What does it mean if the reaction moves to the left?

A

More reactants and it is a reverse reaction

40
Q

What does increase in temperature mean for reversible reaction?

A

Moves in direction of endothermic reaction to reverse the change.
This is because the temperature needs to be decreased and endothermic absorbs energy.

41
Q

What does decrease in temperature mean for reversible reaction?

A

Moves in direction of exothermic reaction to reverse the change
This is because the temperature needs to be increased and exothermic releases energy.

42
Q

What does increase in pressure mean for reversible reaction?

A

Moves in direction of the forward reaction (right) and number of products increase.
This is because products take up less space and it is opposing by making fewer molecules

43
Q

What does decrease in pressure mean for reversible reaction?

A

Moves in direction of the reverse reaction (left) and number of reactants increase.
This is because products take up less space and it is opposing by making more molecules

44
Q

What does increase in concentration of reactant mean for reversible reaction?

A

equilibrium shifts to right (more forward reaction)

45
Q

What does increase in concentration of product mean for reversible reaction?

A

equilibrium shifts to left (more reverse reaction)

46
Q

How do catalysts affect equilibrium?

A

Does not affect the position of equilibrium. It increases 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

47
Q

What is the Haber process?

A

The manufacturing of ammonia from nitrogen and hydrogen in an exothermic reaction (ΔH=-92kJ/mol)

48
Q

What is hydrogen obtained from?

A

Methane (natural gas)

49
Q

What is nitrogen obtained from?

A

Air

50
Q

What is the balanced symbol equation for haber process

A

N2(g) + 3H2(g) ⇌ 2NH3(g)

51
Q

What happens upon cooling in the haber process?

A

Ammonia is liquified and removed and the remaining nitrogen and hydrogen is recycled

52
Q

What pressure is the haber process done at?

A

200atm. Higher pressure increases yield but 400atm needs powerful pumps so 200atm is safer and saves money

53
Q

What temperature is the haber process done at?

A

450°C
Exothermic reactions favour lower temperatures but the reaction is too slow while the higher temperature proceeds at faster rate but yield is low.

54
Q

What does the haber process do to improve yield?

A
  • Moderately high pressure (200atm)
  • Remove ammonia
55
Q

What does the haber process do to improve reaction rate?

A
  • moderately high temperature (450°C)
  • Use catalyst (iron)
56
Q

What is the catalyst in the haber process?

A

iron

57
Q

What is the contact process?

A

Used to manufacture raw concentrated sulfuric acid which is used in car batteries, making fertilisers, soaps and detergents

58
Q

What is the first stage of the contact process?

A

The first stage is the production of sulfur dioxide. Sulfur is burned in air
S + O2 → SO2
sulfur + oxygen → sulfur dioxide

59
Q

What is the second stage of the contact process?

A

The main stage is the oxidation of sulfur dioxide to sulfur trioxide using a vandium(V) oxide, V2O5, catalyst
2SO2 + O2 ⇌ 2SO3
sulfur dioxide + oxygen ⇌ sulfur trioxide
(exothermic reaction -196kJ/mol, pressure 2atm, temp 450°C)

60
Q

What is the third stage of the contact process?

A

Sulfur trioxide is mixed with dilute sulfuric acid to produce oleum
SO3 + H2SO4 → H2S2O7 (oleum)

61
Q

What is oleum?

A

fuming sulfuric acid
H2S2O7

62
Q

What is the final stage of the contact process?

A

Oleum is mixed with water to produce 99% concentrated sulfuric acid
H2S2O7 + H2O -> 2H2SO4

63
Q

Why is the temperature 450°C in contact process?

A

High temperature decreases yield (favours endothermic) yet low temperatures gives low rate of reaction. 450 ºC is a compromise temperature between having a lower yield of products but being made more quickly. Also the catalyst doesn’t work under 400 degrees

64
Q

Why is the pressure 2atm in contact process?

A

The position of the equilibrium is already to the right so high pressure is expensive and unnecessary

Chemistry IG (14 decks)

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