Hydrazine (N2H4\text{N}_2\text{H}_4N2H4) is a highly reactive liquid used as a rocket propellant. Direct measurement of its standard enthalpy of formation is difficult, but it can be determined using Hess's law and standard enthalpies of combustion:
N2H4(l)+O2(g)→N2(g)+2H2O(l)ΔH⊖=−622 kJ mol−1 \text{N}_2\text{H}_4(\text{l}) + \text{O}_2(\text{g}) \rightarrow \text{N}_2(\text{g}) + 2\text{H}_2\text{O}(\text{l}) \quad \Delta H^\ominus = -622\text{ kJ mol}^{-1} N2H4(l)+O2(g)→N2(g)+2H2O(l)ΔH⊖=−622 kJ mol−1 H2(g)+12O2(g)→H2O(l)ΔH⊖=−286 kJ mol−1 \text{H}_2(\text{g}) + \frac{1}{2}\text{O}_2(\text{g}) \rightarrow \text{H}_2\text{O}(\text{l}) \quad \Delta H^\ominus = -286\text{ kJ mol}^{-1} H2(g)+21O2(g)→H2O(l)ΔH⊖=−286 kJ mol−1What is the standard enthalpy of formation of liquid hydrazine (in kJ mol−1\text{kJ mol}^{-1}kJ mol−1), as represented by the following equation?
N2(g)+2H2(g)→N2H4(l) \text{N}_2(\text{g}) + 2\text{H}_2(\text{g}) \rightarrow \text{N}_2\text{H}_4(\text{l}) N2(g)+2H2(g)→N2H4(l)+336+336+336
+50+50+50
−50-50−50
−1194-1194−1194
34 exam-style questions on AQA A Level Chemistry Energetics, covering Enthalpy change, Calorimetry, Applications of Hess's law, and Bond enthalpies. Each one has a worked solution and a mark scheme showing where the marks go.