Question

what is change in Enthalpy?how does it help to identify the type of thermo chemical reaction​

Answer 1

Answer:

Enthalpy is a measure of internal energy of a system. If the above value is negative then the reaction is exothermic heat is released. At constant pressure when a reaction occurs heat is released or absorbed. This amount of heat released or absorbed is called enthalpy change.

Answer 2

Answer:

Physical and chemical changes are done under constant pressure. Gained or lost heat in reactions under constant pressure is called enthalpy change. Enthalpy is the total kinetic and potential energy of particles of matter. It is denoted by letter "H". Enthalpy of matters can not be measured, however, enthalpy change can be measured. We can find change in enthalpy as given below;

Reactants → Products

If HR is the enthalpy of reactants and HP is the enthalpy of products, change in enthalpy becomes,

∆H=HP-HR

In exothermic reactions, HR is larger than HP, so enthalpy change becomes negative

HP<HR so; ∆H<0

Since endothermic reactions absorb heat, HP>HR and enthalpy change becomes positive.

HP>HR so; ∆H>0

Enthalpy change depends on temperature and pressure. Thus, you should compare enthalpy changes of reactions under same temperature and pressure.

Enthalpy change under 1 atm pressure and 25 0C temperature is called standard enthalpy change.