AeroLab Reading room

CHEM / AS level

Rates and inorganic periodic trends

Collision energy distributions explain why temperature affects rate. Catalysts lower activation energy but do not make every collision productive.

Learning objectives

The big idea

Collision energy distributions explain why temperature affects rate. Catalysts lower activation energy but do not make every collision productive.

Period 3 trends, Group 2 compounds, nitrogen and sulfur chemistry connect structure to reactivity. Compare reactions and conditions explicitly; a periodic trend is a pattern with a chemical explanation, not merely a memorised arrow.

Worked example

Which generally increases reaction rate: raising temperature or lowering it?

Follow the solution

A larger fraction of collisions exceeds activation energy, often strongly increasing rate.

Investigate and explain

Predict the worked result before calculating. Change one input, record the new result, and explain which assumptions still hold.

Use the evidence activity below; no exact PhET model is claimed.

Open the interactive investigation

Check your understanding

1. Across a period, what generally happens to atomic radius?

  1. It always doubles
  2. It becomes zero
  3. It decreases
Check the answer and reasoning

It decreases

Increasing nuclear charge attracts electrons in the same main shell more strongly, with limited extra shielding.

2. Which generally increases reaction rate: raising temperature or lowering it?

  1. Raising temperature
  2. Lowering temperature
  3. Neither can affect rate
Check the answer and reasoning

Raising temperature

A larger fraction of collisions exceeds activation energy, often strongly increasing rate.

3. Does a catalyst increase the energy of every reacting particle?

  1. Yes
  2. No
  3. Only a metal catalyst
Check the answer and reasoning

No

It provides another pathway with lower activation energy rather than heating all particles.