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GCSE Triple Chemistry > Rates and Extent of Chemical Change > Flashcards

Rates and Extent of Chemical Change Flashcards

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1
Q

How do you calculate the mean rate of reaction?

A

quantity of products formed / time

or

quantity of reactants used / time

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2
Q

Why do reactions start off with a high rate?

A

Because they have a lot of reactant particles

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3
Q

Why is it hard to find the rate of reaction at a certain point from a graph?

A

The gradient of the graph is constantly changing

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4
Q

How do scientists determine the rate of reaction at a certain point?

A

Draw a tangent and find the gradient

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5
Q

What is meant by collision theory?

A

Chemical reactions can only take place when reacting particles collide with sufficient energy to react.

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6
Q

According to collision theory, what determines the rate of a reaction?

A

The frequency of successfull collisions

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7
Q

Explain using collision theory why the rate of reactions slow with time

A

At the beginning of the reaction there are lots of reactant particles colliding with each other so the rate is high. As the reaction progresses there are less reactant particles colliding with each other because they have already reacted

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8
Q

What effect does concentration/pressure have on the rate of reaction?

A

Higher concentration/pressure means a higher rate

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9
Q

Why does a higher concentration/pressure mean a higher rate of reaction?

A

Because there are more particles so the frequency of successful collisions will be higher and therefore the rate

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10
Q

What effect does surface area have in rate?

A

Higher surface area = higher rate of reaction

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11
Q

Why does higher surface area increase the rate?

A

Because there is more surface for the particles to react with and therefore more frequent successful collisions

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12
Q

Name a control variable in the disappearing cross experiment

A

Size of the cross, Volume of reactants

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13
Q

Name an independent variable in the Disappearing cross experiment

A

Concentration of reactants

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14
Q

Name the dependent variable in the disappearing cross experiment

A

The time it takes for the cross to disappear

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15
Q

What is meant by Activation energy?

A

The minimum amount of energy that particles must have in order to react

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16
Q

What effect does temperature have on rate?

A

Increasing the temperature increases the rate

17
Q

Why does rate increase with temperature (2 reasons)?

A
  1. Because particles have more energy and are moving faster so the frequency of collisions increases
  2. Because each collision has more energy so more particles have sufficient activation energy
18
Q

Endo or Exo?

A

Endothermic

19
Q

Endo or Exo?

A

Exothermic

20
Q

What do catalysts do?

A

Increase the rate of reaction without being used up

21
Q

How do Catalysts increase the rate?

A

They provide a different pathway for the reaction with lower activation energy meaning more successful collisions occur

22
Q

What is a Reversible reaction?

A

One where the products can react to reform the reactants

23
Q

Give two examples of reversible reactions

A
  • Haber Process
  • Heating hydrated copper sulfate
24
Q

How do we change the direction of a reversible reaction?

A

Change the conditions

25
Q

If the forward reaction is endothermic the backward one is….?

A

exothermic

26
Q

What does Le Chatelier’s Principle say about reversible reactions

A

If you try and change the conditions of a reversible reaction at equilibrium the system with try to counteract the change

27
Q

What happens if you increase the temperature in a reversible reaction?

A

The system favours the endothermic direction

28
Q

What happens if you decrease the temperature in a reversible reaction?

A

The system favours the exothermic direction

29
Q

What happens if you decrease the pressure in a reversible reaction?

A

The system favours the side with more gas particles

30
Q

What happens if you increase the pressure in a reversible reaction?

A

The system favours the side with less gas particles

31
Q

What happens when you increase the concentration of reactants in a reversible reaction?

A

The system makes more products

GCSE Triple Chemistry (9 decks)

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