Question

Enthalpy of dilution of 4M HCl to 2M HCl is -2.5kJ/mol. Find the enthalpy change when 500 mL of HCl is diluted from 4M to 2M.
A. -2.5kJ/mol
B.-5.0kJ/mol
C.-10kJ/mol
D.-1.25kJ/mol

Answer 1

Hint: The Enthalpy of the reaction is defined as the addition of the internal energy and product of pressure and volume. Enthalpy is the state function that depends on the state functions temperature, pressure, and internal energy.

Complete step by step answer:
The amount of heat released or absorbed during a chemical reaction at constant pressure is said as enthalpy change of the reaction. The enthalpy change is denoted by $\Delta H$.
The formula for the calculation of enthalpy change is shown below.
$\Delta H = \Delta U + P\Delta V$
Where
$\Delta H$ is the enthalpy.
$\Delta U$ is internal energy.
P is the pressure.
$\Delta V$ is the volume.
Given, the enthalpy of dilution of 4M to 2M HCl is -2.5 kJ/mol.
M means molarity of solution which is given in terms of moles per liter. The dilution of 4 M solution in 1000 L is done to 2M. The enthalpy change is -2.5 kJ/mol.
When 500 mL of HCl is diluted from 4M to 2M, the enthalpy change will be the same as the enthalpy change does not depend on temperature.
Thus, enthalpy change on diluting 500 mL of HCl from 4M to 2M is -2.5 kJ/mol.

Thus, the correct option is option (A).

Note:
The enthalpy change is only possible in the reactions where pressure is kept constant. The enthalpy is negative when the energy is released which means the reaction is exothermic.