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

In an enthalpy profile for the reaction A → B, the enthalpy of A is $+50 \ \text{kJ mol}^{-1}$, the enthalpy of B is $-20 \ \text{kJ mol}^{-1}$, and the activation energy for the forward reaction is $+80 \ \text{kJ mol}^{-1}$. What is the activation energy for the reverse reaction B → A?

An enthalpy profile for the combustion of methane, $\text{CH}_4\text{(g)} + 2\text{O}_2\text{(g)} \rightarrow \text{CO}_2\text{(g)} + 2\text{H}_2\text{O(l)}$, shows the reactants at $0 \ \text{kJ mol}^{-1}$, the transition state at $+265 \ \text{kJ mol}^{-1}$, and the products at $-890 \ \text{kJ mol}^{-1}$. Which statement about this reaction is correct?

An enthalpy profile shows reactants at $0 \ \text{kJ mol}^{-1}$, products at $-150 \ \text{kJ mol}^{-1}$, and an activated complex at $+80 \ \text{kJ mol}^{-1}$. Which statement about this reaction is correct?

The reaction between zinc metal and aqueous copper(II) sulfate is represented by: $$\text{Zn(s)} + \text{CuSO}_4\text{(aq)} \rightarrow \text{ZnSO}_4\text{(aq)} + \text{Cu(s)} \quad \Delta H = -220 \text{ kJ mol}^{-1}$$ Which statement correctly describes the enthalpy profile for this reaction?