Question

Which of the following is/are thermochemical reaction(s)?

• A. $\text{CaO(s)}+{\text{H}}_2\text{O(l)}\to {\text{Ca(OH)}}_2\text{(aq)}$
• B. $\text{Cu(s)}+{\text{Zn(SO)}}_4\text{(aq)}\to {\text{Cu(SO)}}_4\text{(aq)}+\text{Zn(s)}$
• C. $2\text{Na(s)}+2{\text{H}}_2\text{O(l)}\to 2\text{NaOH(aq)}+{\text{H}}_2\text{(g)}$
• D. ${\text{H}}_2\text{(g)}+{\text{Cl}}_2\text{(g)}\to 2\text{HCl(g)}$

Answer 1

Answer: (A), (C), (D)

${\text{H}}_2\text{(g)}+{\text{Cl}}_2\text{(g)}\to 2\text{HCl(g)}$

$\text{CaO(s)}+{\text{H}}_2\text{O(l)}\to {\text{Ca(OH)}}_2\text{(aq)}$ $CaO\left(s\right)+H_{2}O\left(l\right)\to Ca\left(OH{)}_2\right(aq)$

$2\text{Na(s)}+2{\text{H}}_2\text{O(l)}\to 2\text{NaOH(aq)}+{\text{H}}_2\text{(g)}$

${\text{H}}_2\text{(g)}+{\text{Cl}}_2\text{(g)}\to 2\text{HCl(g)}$

In the above chemical reactions, heat is released during the reaction. These type of reactions in which heat is either released or absorbed are called as a thermochemical reaction.

Moreover, the reaction of copper with zinc sulphate will not occur and the one mentioned is incorrect as copper is less reactive than zinc so it cannot displace zinc from its aqueous solution.