Question

Match the following associations. Exothermic or endothermic

Answer 1

Answer:

1) ∆H is positive $\Rightarrow$ Endothermic

2) $E_p>E_r$ $\Rightarrow$ Endothermic  

3) Energy is absorbed $\Rightarrow$ Endothermic

4) $E_r>E_p$ $\Rightarrow$ Exothermic

5) ∆H is negtive $\Rightarrow$ Exothermic

Explanation:

∆H is called as enthalpy change  

It is also called as Heat of reaction

Energy is required for the bond to break a bond.

Energy is released when a bond is formed.

$H_2+Cl_2>2HCl$

that is

$H-H+Cl-Cl>2H-Cl$

We see in this equation, bonds between hydrogen and chlorine molecules gets broken and on the right side bond is formed in HCl.

If energy of products greater than energy of reactants then the reaction enthalpy change is endothermic .

If energy of products lesser than energy of reactants then the reaction enthalpy change is exothermic .

For example  

$\Delta H=E_p-E_r$

$=30KJ-20KJ$

$=+10KJ$

(positive hence endothermic)

$\Delta H=E_p-E_r$

$=10KJ-40KJ$

$=-30KJ$

(negative hence exothermic)