For an exothermic reaction the change in enthalpy is ________.

Question

Question

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NHPC JE Mechanical 6 April 2022 (Shift 1) Official Paper

Answer 1

Explanation:

Exothermic reaction: it is the reaction in which heat goes out from the system or heat is dissipated from the system.

The change in enthalpy is negative in exothermic reaction ΔH < 0.
It is because the energy released by the reaction is more than the energy used by the reaction.
In thermodynamics generally when heat flows out of the system, the sign convention we use is negative.

Change in enthalpy:

In chemical reactions enthalpy changes is equal to the difference between energy used to break bonds and energy gained by the formation of new bonds.
It describes the energy change at constant pressure.
at constant pressure from first law of thermodynamics (δQ)_p = dh
sign convention for heat dissipation from the system δQ < 0 ⇒ dh < 0