GCSE Combined Science Rates & equilibrium questions by topic

This question is about calculating and measuring rates.

1. (a)Write the equation for the mean rate of a reaction.[1]
2. (b)A reaction loses 0.80 g of gas in 50 s. Calculate the mean rate.[2]
3. (c)Name the equipment used to collect and measure the volume of gas made.[1]

A student wants to make a reaction between a solid and an acid go faster.

1. (a)State two changes that would increase the rate.[2]
2. (b)Explain one of your choices using collision theory.[2]

This question is about catalysts.

1. (a)State what a catalyst does.[2]
2. (b)Give one everyday or industrial example of a catalyst at work.[1]
3. (c)State what happens to the mass of a catalyst after the reaction.[1]

Blue hydrated copper(II) sulfate is heated in a test tube, then water is added to the white solid left behind.

1. (a)Describe the colour change when the crystals are heated.[2]
2. (b)Name the substance added to reverse the change.[1]
3. (c)State the term for a reaction that runs in both directions.[1]

Two runs react identical magnesium strips with excess acid. Run A uses 1.0 mol/dm³ acid and collects 40 cm³ in 50 s; Run B uses 2.0 mol/dm³ acid and collects 40 cm³ in 25 s.

1. (a)Calculate the mean rate of each run.[2]
2. (b)Compare the two rates.[1]
3. (c)Explain why both runs eventually collect the same total volume of gas.[2]

This question is about tangents on rate curves.

1. (a)Describe how to find the rate of reaction at 40 s from a curve.[2]
2. (b)A tangent at 40 s rises 28 cm³ over 14 s. Calculate the rate at 40 s.[2]
3. (c)State the rate once the curve has gone flat.[1]

Disappearing-cross results: 0.5 mol/dm³ → 90 s; 1.0 mol/dm³ → 45 s; 1.5 mol/dm³ → 30 s; 2.0 mol/dm³ → 22 s.

1. (a)State which concentration reacted fastest.[1]
2. (b)Calculate 1/time for the 1.0 mol/dm³ run.[2]
3. (c)State the pattern linking concentration and rate suggested by the data.[2]

(Higher) This question is about equilibrium.

1. (a)Describe what is meant by dynamic equilibrium.[2]
2. (b)State the rule for predicting how an equilibrium responds to a change in conditions.[1]
3. (c)Predict and explain the shift when the pressure is increased on N₂(g) + 3H₂(g) ⇌ 2NH₃(g).[2]

Design and evaluate an investigation into how acid concentration changes the rate of a magnesium reaction using a gas syringe.

1. (a)Describe the method.[3]
2. (b)Explain why results are compared using 1/time.[1]
3. (c)Name two variables that must be controlled.[2]

A gas-syringe experiment gives: 0 s → 0 cm³, 10 s → 34 cm³, 20 s → 56 cm³, 30 s → 68 cm³, 40 s → 72 cm³, 50 s → 72 cm³.

1. (a)Calculate the mean rate over the first 10 s.[1]
2. (b)Calculate the mean rate between 30 s and 40 s.[1]
3. (c)Explain why the rate fell between these intervals.[2]
4. (d)State when the reaction finished.[1]
5. (e)State the total volume of gas the reaction produced.[1]

(Higher) Hydrated copper(II) sulfate sits in equilibrium: hydrated (blue) ⇌ anhydrous + water. Heating is the endothermic forward change.

1. (a)Describe the observations when the blue crystals are heated and when water is then added.[2]
2. (b)Explain, using the opposing-changes rule, why adding water turns the powder blue.[2]
3. (c)Explain why adding a catalyst would not change the position of this equilibrium.[2]

The same magnesium ribbon reacts with excess hydrochloric acid at 20 °C and at 40 °C, both traced on gas-volume graphs.

1. (a)Describe how the two curves differ at the start.[2]
2. (b)Explain the difference using collision theory.[2]