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GCSE Chemistry > Topic 7: Rates of Reaction and Energy Changes > Flashcards

Topic 7: Rates of Reaction and Energy Changes Flashcards

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1
Q

What does rate of reaction mean?

A

How quickly a reaction happens

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2
Q

What are the 2 ways that rate of reaction can be calculated?

A
  1. rate of reaction = amount of product formed/time
    OR
  2. rate of reaction = amount of reactant used/time
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3
Q

What are the common units of rate of reaction?

A

g/s
cm3/s
mol dm3/s

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4
Q

What are the 3 ways to measure rate of reaction?

A
  1. Time it takes for the reactants to form a precipitate
  2. The change in mass over time (mass after reaction - mass before reaction)
  3. Volume of gas produced over time
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5
Q

What goes on the x axis and on the y axis of a rate of reaction graph?

A

Y axis - amount of product formed
X axis - time

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6
Q

What does a steep line show on a rate of reaction graph?

A

A faster rate of reaction

(The steep the line, the faster the rate of reaction)

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7
Q

What do flat lines show on a rate of reaction graph?

A

The reaction has finished

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8
Q

If more reactant is used in a reaction, how does it affect how much product is formed?

A

The more reactants used, the more products formed

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9
Q

How can you find the rate of reaction on a rate of reaction graph?

A

The gradient

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10
Q

How to calculate gradient?

A

Gradient = change in y/change in x
OR
Gradient = rise/run

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11
Q

What’s the process to find the rate of reaction at a specific point (if it’s on a curve) on a rate of reaction graph?

A
  1. Draw a tangent to the curve at that point
  2. Then create triangle in dotted lines - to find the gradient
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12
Q

What are the 4 factors affecting rates of reaction?

A
  1. Temperature
  2. Pressure or concentration
  3. Surface area
  4. Catalysts
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13
Q

What is activation energy?

A

The minimum amount of energy that particles need to react

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14
Q

What 2 things does rate depend on with collision theory?

A

Collision frequency - the more collisions between particles, the faster the rate of reaction
&
Collision energy - the more collisions with at least the activation energy, the faster the rate of reaction

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15
Q

If there is high energy and high frequency when particles collide, what happens to the rate of reaction?

A

The rate of reaction is fast

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16
Q

If there is low energy and low frequency when particles collide, what happens to the rate of reaction?

A

The rate of reaction is slow

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17
Q

If a reaction is done at a high temperature, what happens to the rate of reaction? Why?

A

The rate of reaction is fast - particles move faster - collide more frequently with more heat energy

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18
Q

If the reaction is done at a cold temperature, what happens to the rate of reaction? Why?

A

The rate of reaction is slow - particles move slower - collide less frequently with less heat energy

19
Q

If the reaction is done at a high pressure or concentration, what happens to the rate of reaction? Why?

A

The rate of reaction is fast - the more particles in the same volume, the more frequent the collisions

20
Q

If the reaction is done at a low pressure or concentration, what happens to the rate of reaction? Why?

A

The rate of reaction is slow - the less particles in the same volume, the less frequent the collisions

21
Q

If the reaction has particles with a small surface area in the reaction, what happens to the rate of reaction? Why?

A

The rate of reaction is fast - more area for particles to collide with - more frequent collisions

22
Q

If the reaction has particles with a large surface area in the reaction, what happens to the rate of reaction? Why?

A

The rate of reaction is slow - less area for particles to collide with - less frequent collisions

23
Q

As size of particles in a reaction decreases, what happens to the surface area to volume ratio?

A

The surface area to volume ratio is larger - less surface area of particles within a large volume

24
Q

What is a catalyst?

A

Speeds up a reaction without being chemically changed or used up in the reaction, and without changing the products

25
Q

What happens to activation energy when a catalyst is used in a reaction? Why?

A

It’s lower - allows more collisions to have energy to react with each other - increases rate of reaction

26
Q

What is an example of a catalyst? What’s a use for it?

A

An enzyme - used to make alcoholic drinks

27
Q

What 2 types of energy transfers are there?

A
  1. Endothermic reaction
  2. Exothermic reaction
28
Q

What is an endothermic reaction?

A

A reaction that takes in heat energy from the surroundings

29
Q

What is an endothermic reaction shown by?

A

A decrease in temperature

30
Q

What is an exothermic reaction?

A

A reaction that gives out heat energy to the surroundings

31
Q

What is an exothermic reaction shown by?

A

An increase in temperature

32
Q

What equipment is used during the measuring of a temperature change?

A
  1. A thermometer - to measure the temperature
  2. Large beaker with a polystyrene cup (with reaction mixture in it and a lid on it) in it
  3. Cotton wool around the polystyrene cup - to insulate it
33
Q

How can temperature change be measured?

A
  1. Record initial temperature
  2. Record maximum temperature reached
  3. Then do: maximum temperature reached - initial temperature
34
Q

What 2 things can the polystyrene cup method, that measures temperature change, be used for?

A
  1. Dissolving salts in water
  2. Neutralisation, displacement and precipitation reactions
35
Q

What does the reaction profile of an endothermic reaction look like (talk about: activation energy, energy of reactants and energy of products)?

A

Activation energy: high
Energy of reactants: low
Energy of products: high

36
Q

If a reaction profile shows a reaction where the PRODUCTS HAVE MORE energy than the reactants, what type of reaction is it? Has energy been absorbed or released?

A

Endothermic reaction - energy has been absorbed

37
Q

What does the reaction profile of an exothermic reaction look like (talk about: activation energy, energy of reactants and energy of products)?

A

Activation energy: low
Energy of reactants: high
Energy of products: low

38
Q

If a reaction profile shows a reaction where the REACTANTS HAVE MORE energy than the products, what type of reaction is it? Has energy been absorbed or released?

A

Exothermic reaction - energy has been released

39
Q

Do endothermic reactions break or form bonds?

A

They break bonds

40
Q

Do exothermic reactions break or form bonds?

A

They form bonds

41
Q

What is an example of an endothermic reaction?

A

Photosynthesis

42
Q

Why do endothermic reactions break bonds?

A

Because energy used to break bonds is greater than energy released by forming new bonds in endothermic reactions

43
Q

Why do exothermic reactions form bonds?

A

Because energy released by forming bonds is greater than energy used to break existing bonds in exothermic reactions

44
Q

How can overall energy change be calculated?

A

Overall energy change = total energy needed to break bonds - total energy released by forming bonds

GCSE Chemistry (9 decks)

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