Science Double Award Co-Ordinated (0654) iGCSE 2026 Chemistry 6 (Chemical Reaction)

How does increasing the concentration of a solution affect the rate of reaction?

It increases the rate because there are more reactant particles per unit volume, leading to more frequent collisions.

How does increasing the pressure of a gas affect the rate of reaction?

It increases the rate because the particles are closer together, leading to more frequent collisions.

How does increasing the surface area of a solid affect the rate of reaction?

It increases the rate because more particles are exposed, allowing more collisions to occur.

How does increasing the temperature affect the rate of reaction?

It increases the rate because particles gain more kinetic energy, moving faster and colliding more frequently with greater energy.

What is the effect of adding a catalyst on the rate of reaction?

A catalyst increases the rate by providing an alternative pathway with lower activation energy (Ea), without being used up.

What happens to a catalyst at the end of a reaction?

It remains unchanged and can be reused.

How does a catalyst affect activation energy (Ea)?

A catalyst lowers activation energy, making it easier for particles to react.

What are two practical methods to measure the rate of a reaction?

1. Measuring the change in mass of a reactant or product. 2. Measuring the volume of gas produced over time.

How can gas evolution be used to measure reaction rate?

Collect and measure the volume of gas produced at regular time intervals. Faster gas production means a higher reaction rate.

How can change in mass be used to measure reaction rate?

Place the reaction on a balance and measure the mass decrease over time as gas escapes. A faster decrease means a higher reaction rate.

What does a steeper slope on a rate of reaction graph indicate?

A faster reaction rate because more reactants are reacting quickly.

According to collision theory, what must happen for a reaction to occur?

Particles must collide with enough energy (≥ Ea) and in the correct orientation.

How does increasing concentration affect the rate of reaction using collision theory?

More particles per unit volume → higher collision frequency → faster reaction.

How does increasing pressure affect the rate of reaction using collision theory?

Gas particles are closer together → higher collision frequency → faster reaction.

How does increasing surface area affect the rate of reaction using collision theory?

More exposed particles → higher collision frequency → faster reaction.

How does increasing temperature affect the rate of reaction using collision theory?

Particles move faster → higher collision frequency and more collisions with enough energy → faster reaction.

How does a catalyst affect the rate of reaction using collision theory?

A catalyst provides an alternative reaction pathway with lower activation energy, so more particles have enough energy to react.

What is oxidation?

Gain of oxygen.

What is reduction?

Loss of oxygen.

What is a redox reaction?

A reaction where oxidation and reduction happen simultaneously.

How can you identify a redox reaction using oxygen?

One substance gains oxygen (oxidation), while another loses oxygen (reduction).

In the reaction 2Mg + O₂ → 2MgO, which substance is oxidized and which is reduced?

Magnesium (Mg) is oxidized (gains oxygen), and oxygen (O₂) is reduced (forms MgO).

What is oxidation in terms of electrons?

Loss of electrons.

What is oxidation in terms of oxidation number?

Increase in oxidation number.

What is reduction in terms of electrons?

Gain of electrons.

What is reduction in terms of oxidation number?

Decrease in oxidation number.

What is a redox reaction in terms of electron transfer?

A reaction where one substance loses electrons (oxidation) and another gains electrons (reduction).