Worksheet Chapter 3: Thermochemistry

1. Fill in the blank: A chemical reaction that absorbs heat energy from its surroundings is classified as an ________ reaction.

2. Explain why the theoretical heat of combustion of propanol obtained from a school laboratory experiment is usually significantly lower than the standard textbook data value.

3. 50 cm³ of 2.0 mol dm⁻³ nitric acid (HNO₃) is mixed with 50 cm³ of 2.0 mol dm⁻³ potassium hydroxide (KOH) solution in a polystyrene cup. The initial temperature of both solutions is 28.0 °C and the highest temperature reached is 41.5 °C. Calculate the heat of neutralisation. [c = 4.2 J g⁻¹ °C⁻¹, Density = 1.0 g cm⁻³]

4. True or False: Bond formation is an endothermic process because energy is required to bring atoms together.

5. When 50 cm³ of 1.0 mol dm⁻³ copper(II) sulfate solution reacts with excess zinc powder, the temperature increases by 10 °C. Calculate the heat released in Joules. [Specific heat capacity = 4.2 J g⁻¹ °C⁻¹, Density of solution = 1.0 g cm⁻³]

6. Which of the following best defines the heat of combustion of ethanol?

7. True or False: The heat of neutralisation between ethanoic acid and sodium hydroxide is numerically greater than -57.3 kJ mol⁻¹.

8. Write the ionic equation for the precipitation of lead(II) sulfate from lead(II) nitrate and sodium sulfate solutions.

9. Magnesium powder is added to 100 cm³ of 0.5 mol dm⁻³ iron(II) sulfate solution in a polystyrene cup. The temperature of the mixture rises by 8.0 °C. Write the ionic equation for the displacement reaction, calculate the number of moles of iron displaced, and determine the heat of displacement. [c = 4.2 J g⁻¹ °C⁻¹, Density = 1.0 g cm⁻³]

10. Draw an energy profile diagram for an exothermic reaction. On your diagram, clearly label: (i) Axes (Energy vs Reaction Pathway), (ii) Reactants and Products levels, (iii) Activation energy (Ea), and (iv) Heat of reaction (ΔH).