In an experiment to measure the enthalpy change of a reaction involving gases,

which of the following conditions must always be kept constant?

A) Pressure

B )Temperature

C )Volume

D )Temperature and pressure

### 1 Answer | Add Yours

Enthalpy or heat content of a gaseous system is defined as the sum of the internal energy and the product of its pressure volume.

H = E + PV

Where, E is the internal energy, P is the constant pressure, and V is the volume of the system.

Change in enthalpy ∆H, is defined as the amount of energy exchanged with the surroundings at constant pressure and temperature.

It is expressed as: ∆H = ∆E + P∆V

An apparently similar term, change in energy at constant volume is known as internal energy change ∆E.

Hence the right option here, is thus D).

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