# Heat Of Reaction Formula

## Heat Of Reaction Formula

The Heat Of Reaction Formula, also called reaction enthalpy, is the difference in enthalpy values ​​of a chemical reaction under constant pressure. It is a thermodynamic unit of measurement used to determine the total amount of energy produced or released per mole in a reaction. The heat of a chemical reaction can therefore be defined as the heat released or absorbed into the surroundings while the reaction is taking place at constant pressure and temperature. A joule (J) is a unit used to measure the total amount of heat absorbed or released.

In chemical reactions, heat is mainly transferred between the reaction system as one medium and the environment as the other medium. The amount of heat energy is the same before and after the chemical transformation. In other words, the heat absorbed or lost in the reaction system is the same as the heat absorbed or lost in the environment.

Heat Of Reaction Formula or reaction enthalpy is the change in enthalpy value of a chemical reaction at constant pressure. It is also a thermodynamic unit of measurement used to calculate the amount of energy per mole. This energy is released or produced in a reaction. For more information about the Heat Of Reaction Formula, refer to the Extramarks website.

What Is The Heat Of Reaction?

The heat of a chemical reaction can be defined as heat generated in the environment or absorbed during a chemical reaction occurring at constant pressure and temperature. Measure this unit of thermal joules. In most cases, heat transfer occurs between the reaction system as the medium on the one hand and the environment as the medium on the other.

### The Formula For Heat Of Reaction:

It is important to note that the amount of thermal energy remains the same before and after the chemical transformation. Therefore, the heat lost or gained in the reaction system equals the heat lost or gained in the environment. An exothermic reaction releases heat and raises the temperature of the reaction mixture. Endothermic reactions absorb heat and the temperature of the reaction mixture decreases.

The equation for Heat Of Reaction Formula:

Therefore, the Heat Of Reaction Formula equation is:

Q = m × c × ΔT

Where,

m is the mass of the medium,

c will be the specific heat capacity of the reaction medium

Q heat of reaction

ΔT Media temperature difference. And the formula is:

Heat Of Reaction Formula = ΔH(product) – ΔH(reactant)

ΔH represents the change in calorific value.

### Solved Examples For Heat Of Reaction Formula

Q.1: Using the Heat Of Reaction Formula equation, the combustion of a chemical when a given mass of the chemical is burned in air and the temperature of 200g of water is first raised from 28° C to 42° C. Determine the heat change associated with it. The specific heat of water is given by 4.2Jg−1K−1.

Solution: The parameters specified in the problem are:

m=200g

c=4.2Jg−1K−1. ΔT=42-28

ΔT=14∘Cor14K

This problem causes a certain amount of ethanol to burn and raise the temperature of the water. This means that the heat absorbed by water comes from the combustion reaction of ethanol.

This is because the heat loss in the combustion reaction is equal to the heat gain by water. So the changing amount of heat is:

Q = m × c × ΔT

Q=200×4.2×14

Therefore, Q = 11760 J

Q.2: When sodium chloride is dissolved in 100g of water at 20^{\circ}C, the temperature after stirring well is 16∘C. Calculate the heat change during the dissolution process when the specific heat of the solution is 4.18 Jg−1K−1.

Solution: the given parameters are

m=100g

c=4.18 Jg−1K−1. ΔT=20-16

ΔT=4K

The heat absorbed by salt is the same as the heat lost by water. Thus, we get the formula

Q = m × c × ΔT

Q=100×4.18×41

Therefore, Q = 1672 J

For more such examples on the Heat Of Reaction Formula, students can check the Extramarks website.