a Identify the types of enthalpy changes shown in these equations:i Mg(s) + ½O2(g) → MgO(s)ii C2H4(g) + 3O2(g) → 2CO2(g) + 2H2O(l)iii H2(g) + Cl2(g) → 2HCl(g)
Question
a Identify the types of enthalpy changes shown in these equations:i Mg(s) + ½O2(g) → MgO(s)ii C2H4(g) + 3O2(g) → 2CO2(g) + 2H2O(l)iii H2(g) + Cl2(g) → 2HCl(g)
Solution
i) The equation i Mg(s) + ½O2(g) → MgO(s) represents a formation enthalpy change. This is because it shows the formation of magnesium oxide (MgO) from its elements, magnesium (Mg) and oxygen (O2). The enthalpy change in this case is the heat released or absorbed during the formation of one mole of MgO.
ii) The equation ii C2H4(g) + 3O2(g) → 2CO2(g) + 2H2O(l) represents a combustion enthalpy change. This is because it shows the combustion of ethene (C2H4) in the presence of oxygen (O2) to form carbon dioxide (CO2) and water (H2O). The enthalpy change in this case is the heat released during the combustion process.
iii) The equation iii H2(g) + Cl2(g) → 2HCl(g) represents a bond enthalpy change. This is because it shows the breaking of the diatomic hydrogen (H2) and chlorine (Cl2) molecules and the formation of hydrogen chloride (HCl) molecules. The enthalpy change in this case is the energy required to break the bonds in H2 and Cl2 and the energy released when the bonds in HCl are formed.
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