Question

Which of the reactions are exothermic?
A. 2Mg(s) + O2( g ) -----> 2MgO (s) Δ H = − 1203 kJ/mol
B. NH3 (g) + HCl (g)-----> NH4Cl (s) Δ H = − 176 kJ/mol
C. AgCl (s) ------> Ag + (aq) + Cl − (aq) Δ H = 127 kJ/mol
D. 2 Fe2O3 (s) + 3C (s)-------> 4Fe (s) + 3CO2 (g) Δ H = 468 kJ/mol
E. C(graphite) + O2 (g) -------> CO2 (g) Δ H = − 393.5 kJ/mol
F. CH4 (g) + 2O2 (g) -------> CO2 (g) + 2H2O (l) Δ H = − 891 kJ/mol

Answer 1

Answer:

Reaction A, B, E and F are exothermic reactions.

Explanation:

Exothermic reactions are defined as the reactions in which energy of reactants is more than the energy of the products. In these reactions, energy is released by the system.

The total enthalpy of the reaction $(\Delta H)$ comes out to be negative.

Endothermic reactions are defined as the reactions in which energy of products is more than the energy of the reactants. In these reactions, energy is absorbed by the system.

The total enthalpy of the reaction $(\Delta H)$ comes out to be positive.

So, from the given option reaction which are exothermic are with negative value $(\Delta H)$ that enthalpy of reaction and those are:

1) $2Mg(s) + O_2( g )\rightarrow 2MgO (s)$,ΔH = -1203 kJ/mol

2)$NH_3 (g) + HCl (g)\rightarrow NH_4Cl (s)$,ΔH =-176 kJ/mol

3) $C(graphite) + O_2 (g)\rightarrow CO_2 (g)$,ΔH = -393.5 kJ/mol

4) $CH_4 (g) + 2O2 (g)\rightarrow CO_2 (g) + 2H_2O (l)$,ΔH =-891 kJ/mol