Home / AS & A Level Chemistry 5.1 Enthalpy change, $\Delta H$ Exam Style Practice Questions Paper 1
In an experiment to measure the enthalpy change of neutralisation of hydrochloric acid, \(20\,\mathrm{cm^3}\) of solution containing \(0.04\,\mathrm{mol}\) of HCl is placed in a plastic cup of negligible heat capacity.
A \(20\,\mathrm{cm^3}\) sample of aqueous sodium hydroxide containing \(0.04\,\mathrm{mol}\) of NaOH, at the same initial temperature, is added and the temperature rises by \(15\,\mathrm{K}\).
If the heat capacity per unit volume of the final solution is \(4.2\,\mathrm{J\,K^{-1}\,cm^{-3}}\), what is the enthalpy change of neutralisation of hydrochloric acid?
Correct Answer: \( \boxed{\mathrm{C}} \)
Total volume of solution:
\(\mathrm{20+20=40\,cm^3}\)
Heat released:
\(\mathrm{q=40\times4.2\times15\,J}\)
Moles of water (or HCl) neutralised:
\(\mathrm{0.04\,mol}\)
Therefore, the enthalpy change of neutralisation per mole is:
\(\mathrm{\Delta H=\dfrac{40\times4.2\times15}{0.04}\,J\,mol^{-1}}\)
Therefore, the correct answer is (C).
When \(0.47\,\mathrm{g}\) of a hydrocarbon is completely burnt in air, the energy released heats \(200\,\mathrm{g}\) of water from \(23.7^\circ\mathrm{C}\) to \(41.0^\circ\mathrm{C}\).
What is the energy absorbed, in Joules, by the water?
Correct Answer: \( \boxed{\mathrm{C}} \)
The energy absorbed by water is calculated using:
\(q=mc\Delta T\)
where:
Therefore, \(q=200\times4.18\times17.3\).
Therefore, the correct answer is (C).
When \(1.0\,\mathrm{mol}\) of ethanoic acid, \(\mathrm{CH_3COOH}\), in aqueous solution is neutralised by an excess of aqueous sodium hydroxide, \(55\,\mathrm{kJ\,mol^{-1}}\) of energy is released.
Which statement about this reaction is correct?
Correct Answer: \( \boxed{\mathrm{D}} \)
Bond breaking always requires energy, whereas bond formation releases energy.
In an exothermic reaction, the energy released when new bonds form is greater than the energy required to break the original bonds.
Since \(55\,\mathrm{kJ\,mol^{-1}}\) of energy is released during neutralisation, the reaction is exothermic.
Therefore, the correct answer is (D).