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GCSE Chemistry > 7) Rates of Reaction & Energy Changes > Flashcards

7) Rates of Reaction & Energy Changes Flashcards

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1
Q

What does collision theory explain?

A

How reactions happen and why they happen at different rates

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2
Q

What must collide successfully for chemical reactions to happen?

A

Particles

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3
Q

What is the activation energy?

A

The minimum amount of energy required for particles to collide successfully in order to cause a chemical reaction

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4
Q

How can we increase the rate of a chemical reaction?

A

Increase the number of collisions

Increase the energy of the reactant particles

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5
Q

What factors affect reaction rate?

A

Temperature
Concentration
Surface area
Pressure (for gases)

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6
Q

What can be used to calculate rate of reactions at specific times?

A

A graph

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7
Q

How do you calculate the rate of reaction on a graph?

A

Draw a line tangent to the curve
Work out the gradient of the tangent
rate of reaction = change in y / change in x

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8
Q

What shows a complete reaction on a graph?

A

When the line plateaus

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9
Q

What does the steepness of the gradient tell us about reaction rate?

A

Steeper gradient = faster rate of reaction

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10
Q

What different variables can be put against time on a rate of reacting graph?

A

Mass
Volume
Concentration

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11
Q

How does increasing temperature affect the rate of chemical reactions?

A

Higher temperature = increased collision rate

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12
Q

Why does increasing the temperature increase the rate of collisions?

A

Temperature increases the energy in the reactant particles

Greater proportion of particles have the activation energy needed

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13
Q

How does increasing the concentration of dissolved reactant affect the rate of chemical reactions?

A

Increased concentration = increased collision frequency

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14
Q

The concentration of what affects the rate of chemical reactions?

A

Concentration of dissolved reactant

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15
Q

How does increasing the surface area of solid reactants affect the rate of chemical reactions?

A

Increases collision frequency

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16
Q

How is the surface area of solid reactants often increased?

A

By breaking up solids into smaller lumps such as powders to increase the surface area to volume ratio

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17
Q

The surface area of what affects the rate of chemical reactions?

A

Surface area of solid reactants

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18
Q

What are catalysts?

A

Substances that increase a chemical’s reaction rate without reducing the quantity

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19
Q

What do catalysts do in chemical reactions?

A

Increase the rate of reaction by lowering the activation energy

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20
Q

What are examples of catalysts?

A

Iron is used in the process to make ammonia
Platinum and palladium are used in catalytic converters in cars
Enzymes catalyse reactions in biological systems

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21
Q

What catalyst is used in the process to make ammonia?

A

Iron

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22
Q

What catalysts are used in catalytic converters in cars?

A

Platinum

Palladium

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23
Q

Why aren’t catalysts found in chemical equations?

A

They are not used up in reactions so can be used indefinitely

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24
Q

What do catalysts often need to ensure they work?

A

Cleaning

Regenerating

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25
Q

What does the rate of a chemical reaction tell us?

A

How quickly reactants are converted into products

26
Q

What are drawbacks of reaction rate in industry?

A

Expensive to generate conditions needed for very fast reactions
Safety concerns

27
Q

What are reaction rates in industry a trade-off between?

A

Speed
Cost
Safety

28
Q

What is the experiment to measure gas production (rate of reaction)?

A

1) Set up a beaker connected to a measuring cylinder with water in cylinder
2) Place known mass of marble chips in beaker
3) Pour known concentration and excess volume of acid onto chips
4) Start timer
5) Record volume of gas produced every 5 seconds
6) Plot graph of time against volume of gas

29
Q

What is the independent variable when measuring gas production?

A

Mass of marble chips

30
Q

What is the dependent variable when measuring gas production?

A

Volume of gas produced per 5 seconds

31
Q

How do we see how surface area affects reaction rate?

A

Meaure how much gas is produced when marble chips of different surface areas react with hydrochloric acid

32
Q

What is the experiment to observe a colour change (rate of reaction)?

A

1) Place a beaker on top of a piece of paper with an x in the middle
2) Place the solutions (except acid) in the beaker
3) Pour in acid with a known concentration and start clock
4) Stop clock when cross cannot be seen
5) Repeat for different concentrations of acid
6) Plot graph of time against concentration of acid

33
Q

What is the independent variable when observing a colour change?

A

The acid with a known concentration

34
Q

What is the dependent variable when observing a colour change?

A

Time taken for cross to no longer be seen

35
Q

How do we see how concentration affects reaction rate?

A

Observing the colour change between sodium thiosulfate and hydrochloric acid

36
Q

What reactions cause a change in heat energy to take place?

A

Neutralisation reactions
Precipiation reactions
Displacement reactions
Salt dissolving in water

37
Q

What is a neutralisation reaction?

A

The reaction between an acid and a base

38
Q

What is a precipitation reaction?

A

When two solutions react to make an insoluble salt

39
Q

What is a displacement reaction?

A

When a more reactive metal takes the place of a less reactive metal

40
Q

What happens when salt dissolves in water?

A

Ionic bonds in salt break and the ions become more mobile in solution

41
Q

What is an exothermic reaction?

A

Energy reacting in chemicals is transferred to the surroundings
Increase in temperature

42
Q

What are examples of exothermic reactions?

A

Combustion
Neutralisation
Oxidation
Hand warmers

43
Q

How do hand warmers release energy?

A

Iron oxidation

44
Q

What is an endothermic reaction?

A

Energy from the surroundings is transferred to the reacting chemicals
Decrease in temperature

45
Q

What are examples of endothermic reactions?

A

Citric acid + baking soda
Thermal decomposition
Sports injury packs

46
Q

How do sports injury backs absorb heat?

A

When squeezed forcefully ammonium nitrate and water mix resulting in instant cooling

47
Q

What do bond energies measure?

A

The strength of chemical bonds

48
Q

How do we see if a reaction is exothermic or endothermic?

A

Total bond energies of products - total bond energies of reactants

49
Q

What is energy change measured in?

A

kJ mol^-1

50
Q

How does the overall exothermic energy change of a reaction compare to 0?

A

overall energy change of reaction < 0

Negative energy change

51
Q

How does the overall endothermic energy change of a reaction compare to 0?

A

overall energy change of reaction > 0

Positive energy change

52
Q

What happens to bonds in all chemical reactions?

A

Existing bonds are broken in reactants

New bonds formed in products

53
Q

What does the bond energy determine?

A

The amount of energy used up or released in bond breaking or making

54
Q

What process is bond breaking?

A

Endothermic

Requires energy

55
Q

What process is bond making?

A

Exothermic

Releases energy

56
Q

What is the calculation for energy change?

A

energy change = total bond energies of reactants - total bond energies of products

57
Q

What is on reaction profiles’ axis?

A

x-axis: Progess of reaction

y-axis: Energy level

58
Q

What do reaction profiles tell us?

A

Amount of energy contained in reactants and products
Activation energy of a reaction
Overall energy change in a reaction

59
Q

How do catalysts affect reaction profiles?

A

Lower activation energy

60
Q

Which activation profile has reactants higher than products?

A

Exothermic reaction profiles

GCSE Chemistry (10 decks)

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