Measuring Enthalpy Change · Paper 1 — Free Chemistry SL Practice Questions

In an energy level for a chemical reaction, the reactants are positioned at a higher energy level than the products. Which statement correctly describes this reaction?

A student measures the temperature of a reaction mixture and observes a rise in temperature during a chemical reaction. Which statement correctly explains why this observation indicates an exothermic reaction?

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. Both solutions have an initial temperature of $21.5 \ ^\circ\text{C}$. The maximum temperature recorded after mixing is $28.3 \ ^\circ\text{C}$. 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 $\text{kJ mol}^{-1}$?

In a calorimetry experiment, $0.500\ \text{g}$ of magnesium is added to $100.0\ \text{cm}^3$ of $1.00\ \text{mol dm}^{-3}$ hydrochloric acid in a polystyrene cup. The reaction is: $$\text{Mg(s)} + 2\text{HCl(aq)} \rightarrow \text{MgCl}_2\text{(aq)} + \text{H}_2\text{(g)}$$ The density of the solution is $1.00\ \text{g cm}^{-3}$ and its specific heat capacity is $4.18\ \text{J g}^{-1}\text{K}^{-1}$. The temperature rises by $12.5\ \text{°C}$. Which statement best explains why the enthalpy change calculated from this experiment is likely to be less exothermic than the true value?