Energy Cycles in Reactions · Paper 1 — Free Chemistry HL Practice Questions

A student mixes $50.0 \ \text{cm}^3$ of $1.00 \ \text{mol dm}^{-3}$ hydrochloric acid with $50.0 \ \text{cm}^3$ of $1.00 \ \text{mol dm}^{-3}$ sodium hydroxide solution in a polystyrene cup. Both solutions have an initial temperature of $21.5 \ ^\circ\text{C}$, and the maximum temperature recorded after mixing is $28.0 \ ^\circ\text{C}$. The specific heat capacity of the solution is $4.18 \ \text{J g}^{-1} \text{K}^{-1}$ and its density is $1.00 \ \text{g cm}^{-3}$. What is the molar enthalpy change of neutralisation, in $\text{kJ mol}^{-1}$?

The standard enthalpy of combustion of hydrogen is $-286\ \text{kJ mol}^{-1}$. An enthalpy profile is drawn for the reaction $2\text{H}_2\text{(g)} + \text{O}_2\text{(g)} \rightarrow 2\text{H}_2\text{O(l)}$, with the reactants set at the reference level of $0\ \text{kJ}$. Which statement correctly describes this reaction and its enthalpy profile?

The Haber process reaction $\text{N}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightleftharpoons 2\text{NH}_3\text{(g)}$ is carried out in a thermally insulated (adiabatic) reactor. Which observation would best provide experimental evidence that the forward reaction is exothermic?

A student mixes $50.0 \ \text{cm}^3$ of $1.00 \ \text{mol dm}^{-3}$ hydrochloric acid with $50.0 \ \text{cm}^3$ of $1.00 \ \text{mol dm}^{-3}$ sodium hydroxide in a polystyrene cup of heat capacity $30 \ \text{J K}^{-1}$. The temperature rises by $6.0 \ \text{K}$. Using $q = mc\Delta T$ with $c = 4.18 \ \text{J g}^{-1} \text{K}^{-1}$ and solution density $1.00 \ \text{g cm}^{-3}$, but neglecting the heat absorbed by the cup, what is the error in the student's calculated enthalpy change per mole of water formed?