Pupil sheet · Rates of reaction

Why collisions matter — questions

Name ______________________ Date ____________

Try every question before you use a nudge. Write in full sentences where you are asked to explain.

1. identify

Supplement. What must happen for two particles to react?

Circle one answer.

They must collide head-on, whatever their energy
They must collide with a particle of a catalyst
They must collide with at least the activation energy
They must collide with at least the energy of the products

Nudge (only if you are stuck): Not every collision works.

2. explain

Supplement. Match each change to the best collision-theory explanation of why it speeds up a reaction.

Write the number of the matching option.

A lower activation energy, so more of the collisions succeed
Particles move faster: more frequent collisions, and more of them have at least Ea
More particles exposed on the surface, so collisions are more frequent
More particles per unit volume, so collisions are more frequent

1. More concentrated acid: ______
2. Powder instead of lumps: ______
3. A higher temperature: ______
4. A catalyst: ______
5. A higher pressure of reacting gases: ______

Nudge (only if you are stuck): Three of them give more collisions each second; temperature does that and more.

3. explain

Supplement. An indigestion tablet fizzes faster in water at 45 °C than in water at 15 °C. Explain, using collision theory, why. Give two reasons.

Reason 1

Reason 2

Nudge (only if you are stuck): Think about how often the particles collide, and how hard.

4. identify

Supplement. The diagram shows one reaction by two routes, P and Q, on an energy scale. One route is with a catalyst and the other without. Which row gives the route with the catalyst, its activation energy and ΔH?

A reaction pathway diagram on an energy scale from 0 to 300 kJ/mol, with grid lines every 30. The reactants line is at 120 kJ/mol on the left and the products line at 60 kJ/mol on the right. Two curves join the same two lines: curve P, a solid line, rises over a hump whose top is at 270 kJ/mol; curve Q, a dashed line, rises over a hump whose top is at 210 kJ/mol.

Row	Route with the catalyst	Ea of that route / kJ/mol	ΔH / kJ/mol
A	Q	90	−60
B	Q	210	−60
C	P	150	−60
D	Q	90	+60

Circle one answer.

Nudge (only if you are stuck): Which part of the pathway diagram does a catalyst move, and which parts stay put?

5. explain

Supplement. Sulfur dioxide and oxygen are gases that react together. The gas mixture is squeezed into a smaller volume at the same temperature, and the rate goes up. Which row explains why?

Row	Particles per unit volume	Collisions each second	Share of collisions with at least Ea
A	more	more	the same
B	more	more	larger
C	the same	more	larger
D	the same	the same	larger

Circle one answer.

Nudge (only if you are stuck): Which of the four collision-theory ideas does squeezing a gas change?

6. identify / explain

An iron nail held in a Bunsen flame glows but does not burn. A pad of steel wool (very thin strands of steel, which is mostly iron) held in the same flame burns with bright sparks. (a) Identify the factor that makes the steel wool burn so much faster. (b) Supplement. Explain the difference using collision theory. (c) Supplement. Steel wool does not burn in the air of the room until it is held in the flame. Explain why, using activation energy.

(a) The factor

(b) Supplement: collision theory

Nudge (only if you are stuck): For (c): what must a collision have before particles can react?