Question 11
This question is about enthalpy changes.
(a) When ethanoic acid reacts with sodium hydroxide, the enthalpy change, ∆H, is –56.1 kJ mol–1
CH3COOH(aq) + NaOH(aq) → CH3COONa(aq) + H2O(l)
Calculate the temperature rise when 25 cm3 of 2.0 mol dm–3 aqueous ethanoic acid react with 25 cm3 of 2.0 mol dm–3 aqueous sodium hydroxide.
Assume that both solutions have the same initial temperature, have a density of 1.0 g cm–3 and a specific heat capacity of 4.18 J K–1 g–1
(4)
(b) A student recorded the temperature of aqueous ethanoic acid in a polystyrene cup for three minutes.
At the fourth minute, the student added sodium hydrogencarbonate.
The student stirred the mixture and carried on recording the temperature every minute for several minutes.
The student’s measurements are shown in the graph.
A best-fit line showing the temperature before mixing has been drawn.
Draw an appropriate best-fit line on the graph and use it to find the temperature change at the time of mixing.
(2)
(Total 6 marks)