Imagine you have been given a series of materials to react together and the following enthalpy change data has been recorded. Explain the terms exothermic and endothermic, and identify which of the following are exothermic and endothermic reactions. Ensure that you explain your reasoning.
1. N2 + 2O2 → 2NO2 ΔH = +68kJ mol–1
2. C3H8 + 5O2 → 3CO2 + 4H2O ΔH = -2220kJ mol–1
3. 2H2 + O2 → 2H2O ΔH = -486.3kJ mol–1
4. 2CO2 → 2CO + O2 ΔH = +566kJ mol–1
(B) You have been asked to calculate the enthalpy change in the following reaction: 2Al(s) + Fe2O3(s) → Al2O3(s) + 2Fe(s)
The reaction occurs in the following stages:
1. 2Al(s) + Fe2O3(s) → Al2O3(s) + 2Fe(l) ΔH = -732.5kJ mol–1
2. Al2O3(s) + 2Fe(l) → Al2O3(s) + 2Fe(s) ΔH = -27.6kJ mol–1
3. Al2O3(s) + 2Fe(l) → Al2O3(s) + 2Fe(s) ΔH = -91kJ mol–1
Note stages 2 and 3 look the same, but the reaction is cooling from 1700oC to 25oC and hence the enthalpy change there. Calculate the overall enthalpy change for the reaction.
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