Question

Which enthalpy is always positive?

Answer 1

Hint:Thermodynamics deals with the relationship between heat and other forms of energy. Basically, it describes the conversion of thermal energy into another form of energy.When heat is absorbed or released at constant pressure, then that process is known as enthalpy change. Enthalpy is defined as the sum of internal energy and product of volume and pressure.

Complete step-by-step answer:In the thermodynamics system, enthalpy is the measurement of energy. When a process begins, the evolved heat becomes equal to the change in enthalpy at constant pressure. To calculate enthalpy change, we can write a mathematical expression as:
$\Delta H=\Delta U+P\Delta V$
Where $\Delta H$ is the change in enthalpy, $\Delta U$ is the change in internal energy, $P$ is the pressure and $\Delta V$ is the change in volume.
At constant pressure,
$\Delta H=Q$
Where, $Q$ is heat.
Change in enthalpy is always positive for endothermic reactions. Endothermic reactions are defined as reactions that need external energy to proceed. This external energy can be in the form of heat. Endothermic reactions are nonspontaneous and yield products that are higher in energy than the reactants. Therefore, the change in enthalpy for endothermic reactions is always positive.
For example, we require heat to melt down the ice cube. This process is endothermic in nature.

Note:In this question, we have concluded that enthalpy is always positive for endothermic reactions because the energy of the products is higher than the reactants and heat is absorbed from the surrounding. These types of reactions lower the temperature of the surroundings and create a cool effect.
It is to note that change in enthalpy is defined as the difference between the energy gained during the formation of new chemical bonds and energy used to break bonds at constant pressure. It is denoted with $\Delta H$ .