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AQA GCSE Chemistry > C6 The rate and extent of chemical change > Flashcards

C6 The rate and extent of chemical change Flashcards

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1
Q

How can the rate of a chemical reaction can be found.

A

Quantity of a reactant used over time / Time
or
Quantity of product formed over time / Time

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2
Q

What two units can be used for the rate of a reaction. Explain what each symbol stands for.

A

The units of rate of reaction may be given as g/s or cm3/s.

g = grams

s = time in seconds

cm3 = volume in centimeters cubed

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3
Q

For the Higher Tier, students only.

How can you express rate in terms of moles.

A

The units for rate of reaction in terms of moles is mol/s.

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4
Q

What Factors affect the rate of chemical reactions.

A

Factors which affect the rates of chemical reactions include: the concentrations of reactants in solution, the pressure of reacting gases, the surface area of solid reactants, the temperature and the presence of catalysts.

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5
Q

In what way does temperature affect the rate of a chemical reaction.

A

Increasing the temperature increases the frequency of collisions and make the collisions more energetic, and so increases the rate of reaction.

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6
Q

Explain how changing the concentration of reactants the pressure of reacting gases and the surface area of solids affects the rate of a chemical reaction.

A

Increasing the concentration of reactants in solution, the pressure of reacting gases, and the surface area of solid reactants increases the frequency of collisions and so increases the rate of reaction.

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7
Q

Explain what is meant by surface area.

A

The area of a surface which is exposed.

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8
Q

Give an example where a reaction is faster when the surface area is increased.

A

A specific mass of calcium carbonate ( marble chips). reacts with hydrochloric acid at a much slower rate than the same mass of marble chips which has been crushed into a powder.

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9
Q

How would you measure the rate of the reaction between Zinc and HCl.

A

Measure the volume of gas collected every 20 seconds in a gas syringe.

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10
Q

How would you measure the rate of the reaction between sodium thiosulphate and HCl.

A

Place HCl into a conical flask, place a cross underneath the flask add the Sodium thiosulphate and start the clock. Record the time it takes for the cross to no longer be visable, repeat this for each variable.

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11
Q

What is minimum activation energy.

A

It is the minimu amount of energy that particles must posses when they collide for a reaction to happen.

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12
Q

Explain why a gate made from Iron spindles rusts faster then a gate made from soild iron.

A

The spindles have more surface area.

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13
Q

What are catalysts ?

A

Catalysts change the rate of chemical reactions but are not used up during the reaction. Different reactions need different catalysts.

Enzymes act as catalysts in biological systems.

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14
Q

What are enzymes ?

A

Enzymes act as catalysts in biological systems.

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15
Q

Give an example of an enzyme ?

A

Amylase is an enzyme that breaks down starch into glucose

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16
Q

How do catalysts work ?

A

Catalysts increase the rate of reaction by providing a different pathway for the reaction that has a lower activation energy.

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17
Q

How can a reaction profile for a catalysed reaction can be drawn in the following form:

A
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18
Q

What are reversible reactions.

A

In some chemical reactions, the products of the reaction can react to produce the original reactants. Such reactions are called

reversible reactions.

19
Q

How can a reversible reaction be represented ?

A

The reversible sign is the last equation on the card.

20
Q

If a reversible reaction is exothermic in one direction, it is ……………………….. in the opposite direction.

A

If a reversible reaction is exothermic in one direction, it is endothermic in the opposite direction.

21
Q

Exothermic reactions……………………….heat

A

Give out

22
Q

Endo thermic reactions………………………………….. Heat

A

Take in heat.

23
Q

An exothermic reaction is represented by………?

A

an negative sign in front of the delta H

►

24
Q

An endothermic reaction is represented by………?

A

Put a positive sign in front of the delta H

25
Q

If you increase the temperature for an exothermic reaction which way will the reaction speed up ?

A

The backward reaction will speed up..

26
Q

If you increase the temperature for an endothermic reaction which way will the reaction speed up ?

A

The forward reaction will speed up.

27
Q

If you increase the temperature for an exothermic reaction how will it affect the yield of product. ?

A

The product yield decreases.

28
Q

If you increase the temperature for an endothermic reaction which way will the reaction speed up ?

A

The product will increase.

29
Q
A
30
Q

Higher tier only

What are two disadvantages of carrying out a reaction at a high temperature, if the reaction is exothermic ?

A

There will be a low yield of product and it is expensive to generate the extra heat required.

31
Q

Higher tier only

What are two disadvantages of carrying out a reaction at a low temperature, if the reaction is endothermic ?

A

The yield will be low and the rate of the reaction slow.

32
Q

Higher tier only

What are two advantages of carrying out a reaction at a high temperature, if the reaction is endothermic ?

A

The yield will be high and the rate of the reaction will be fast.

33
Q

Higher tier only

How can scientists make a reaction go faster at a lower temperature ?

A

Use a catalyst

34
Q

Higher tier only

What are two disadvantages of doing a reaction at a high pressure?

A

It can be dangerous, could be explosions and it is expensive to generate high pressures.

35
Q

Higher tier only

Explain how an increase in pressure affects the position of a reaction in equilibrium that has gases as products or reactants?

A

An increase in pressure causes the equilibrium position to shift towards the side with the smaller number of molecules of gas.

36
Q

Higher tier only

Explain how a decrease in pressure affects the position of a reaction in equilibrium that has gases as products or reactants ?

A

A decrease in pressure causes the equilibrium position to shift towards the side with the larger number of molecules of gas.

37
Q

Higher tier

What is Le Chatelier’s Principle.

A

If a system is at equilibrium and a change is made to any of the conditions, then the system responds to counteract the change.

38
Q

Higher tier only

What happens if the concentration of one of the reactants or products is changed

A

If the concentration of one of the reactants or products is changed, the system is no longer at equilibrium and the concentrations of all

the substances will change until equilibrium is reached again.

39
Q

Higher tier

What happens if the concentration of a reactant is increased ?

A

If the concentration of a reactant is increased, more products will be formed until equilibrium is reached again.

40
Q

Higher tier

What happens if the concentration of a reactant is decreased ?

A

If the concentration of a product is decreased, more reactants will react until equilibrium is reached again.

41
Q

Higher tier

What happens if the temperature of a system at equilibrium is increased ?

A

If the temperature of a system at equilibrium is increased:

the relative amount of products at equilibrium increases for an endothermic reaction

• the relative amount of products at equilibrium decreases for an exothermic reaction.

42
Q

Higher tier

What happens if the temperature of a system at equilibrium is decreased ?

A

If the temperature of a system at equilibrium is decreased:

  • the relative amount of products at equilibrium decreases for an endothermic reaction
  • the relative amount of products at equilibrium increases for an exothermic reaction.
43
Q

Higher tier

For gaseous reactions at equilibrium: what happens if the pressure is increase ?

A

an increase in pressure causes the equilibrium position to shift towards the side with the smaller number of molecules as shown by the symbol equation for that reaction

44
Q

Higher tier only

For gaseous reactions at equilibrium: what happens if the pressure is decreased ?

A

A decrease in pressure causes the equilibrium position to shift towards the side with the larger number of moles of gas.

AQA GCSE Chemistry (11 decks)

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