Why heat is evovled during exothermic reaction

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Solution

The reactions in which heat is released are known as exothermic reactions. If less energy is needed to break the original existing bonds of the reactant molecules, than is given out when the new bonds are formed in the product molecules, the reaction is exothermic.

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Similar questions

Q. Assertion :

H_{2} (g) + C l_{2} (g) ⟶ 2 H C l (g) + 185 k J

. This reaction is exothermic. Reason: Heat is being evolved.

Q. Assertion :

C a C O_{3} (s) + 2 H C l (a q) ⟶ C a C l_{2} (a q) + H_{2} C O_{3} (a q)

C a C O_{3} (s) + 2 H^{+} (a q) + 2 C l^{-} (a q) ⟶ [C a^{2 +} (a q) + 2 C l^{-} (a q)] + H_{2} C O_{3} (a q)

Thus, net reaction is

C a C O_{3} (s) + 2 H^{+} (a q) ⟶ C a^{2 +} (a q) + H_{2} C O_{3} (a q)

This is an exothermic reaction (in which heat is evolved) and thus there is thermal decomposition of carbonic acid into gaseous carbon dioxide and water. Reason: Heat evolved in the reaction (exothermic) causes decomposition of

H_{2} C O_{3} (a q)

into

C O_{2} (g)

and

H_{2} O (l)

H_{2} C O_{3} ⟶ H_{2} O (l) + C O_{2} (g)

Thus,

H_{2} C O_{3}

is unstable.

In an exothermic reaction, heat is evolved, and system loses heat to the surrounding. For such system
(a) $q_{p}$ will be negative
(b) $Δ_{r} H$ will be negative
(c) $q_{p}$ will be positive
(d) $Δ_{r} H$ will be positive

Q. In the presence of a catalyst, the heat evolved or absorbed during the reaction:

During an exothermic reaction:

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