Which change does not speed up a reaction between a solid and an acid?

using larger lumps of the solid. Larger lumps have a smaller surface area.

What is true of a catalyst?

It speeds up the reaction and is not used up. It can be recovered unchanged at the end.

Why does a more concentrated solution react faster?

There are more particles in the same volume, so they collide more often. More frequent collisions means a faster reaction.

How does a catalyst work?

It lowers the activation energy. More of the collisions are then successful.

On a graph of volume of gas against time, what does a steeper line show?

a faster reaction. The gas is being made more quickly.

The line on a rate graph goes flat. What has happened?

One of the reactants has been used up. No more product is being made.

Rates of reaction · Cambridge IGCSE Co-ordinated Sciences (Double Award)

In plain words

For particles to react they have to bump into each other, and bump hard enough. Anything that makes those useful collisions happen more often speeds the reaction up: more particles in the space, smaller pieces, more heat, or a catalyst to make it easier.

Three things to know

A reaction goes faster with a higher concentration (or gas pressure), a higher temperature, a larger surface area (smaller pieces) or a catalyst.
Collision theory: particles must collide with at least the activation energy. A faster reaction means more successful collisions each second.
A catalyst speeds up a reaction without being used up, by lowering the activation energy. Follow a rate by measuring the gas given off, or the mass lost, over time.

Worked example

A reaction gives off 60 cm³ of gas in the first 20 s. Find the average rate.

Rate = amount of product ÷ time.
= 60 ÷ 20.
= 3 cm³/s.

Tips and tricks

The full answer for temperature has two parts: the particles collide more often, and more of the collisions have enough energy.
On a graph a steeper line means a faster reaction, and where the line goes flat the reaction has finished.

6 questions, about 2 minutes.

It lands in your notebook with its questions as flashcards.

Rates of reaction: 6 questions and answers

These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.

Which change does not speed up a reaction between a solid and an acid?
- heating the acid
- using more concentrated acid
- using larger lumps of the solid (the answer)
- adding a catalyst
Larger lumps have a smaller surface area.
What is true of a catalyst?
- It is used up in the reaction.
- It speeds up the reaction and is not used up. (the answer)
- It slows the reaction down.
- It makes more product.
It can be recovered unchanged at the end.
Why does a more concentrated solution react faster?
- The particles are bigger.
- The particles have more energy.
- There are more particles in the same volume, so they collide more often. (the answer)
- The activation energy is higher.
More frequent collisions means a faster reaction.
How does a catalyst work?
- It heats the reaction.
- It lowers the activation energy. (the answer)
- It adds more reactant.
- It raises the pressure.
More of the collisions are then successful.
On a graph of volume of gas against time, what does a steeper line show?
- a faster reaction (the answer)
- a slower reaction
- more gas at the end
- a higher temperature at the end
The gas is being made more quickly.
The line on a rate graph goes flat. What has happened?
- The reaction has speeded up.
- One of the reactants has been used up. (the answer)
- The catalyst has been used up.
- The gas has escaped.
No more product is being made.

6 questions

Tap an answer and you’ll see straight away whether it’s right, and why.

Worksheet

4 questions, 9 marks. Write your answers on paper, then check them.

Rates of reaction

Cambridge IGCSE Co-ordinated Sciences (Double Award) 0654 · 9 marks · papermunch.org

Name ______________________________ Date ______________

Explain why powdered calcium carbonate reacts faster with acid than lumps of the same mass.[2]
Show answerHide answer
The powder has a larger surface area, so the acid particles collide with it more often.
I got this one
Explain why raising the temperature increases the rate of a reaction.[3]
Show answerHide answer
The particles have more energy and move faster, so they collide more often, and more of the collisions have at least the activation energy.
I got this one
State what is meant by a catalyst.[2]
Show answerHide answer
A substance that increases the rate of a reaction and is not used up (it is chemically unchanged at the end).
I got this one
A reaction produces 48 cm³ of gas in the first 20 s. Calculate the average rate of reaction.[2]
Show answerHide answer
2.4 cm³/s. 48 ÷ 20.
I got this one

Answers: Rates of reaction

1. The powder has a larger surface area, so the acid particles collide with it more often.
2. The particles have more energy and move faster, so they collide more often, and more of the collisions have at least the activation energy.
3. A substance that increases the rate of a reaction and is not used up (it is chemically unchanged at the end).
4. 2.4 cm³/s. 48 ÷ 20.