What is the Difference Between Heat of Solution and Heat of Reaction

The key difference between heat of solution and heat of reaction is that heat of solution is the amount of heat energy released or absorbed by a chemical system upon formation of a solution, whereas heat of reaction is the difference between total reactant and total product molar enthalpies that are calculated for chemical substances in the standard state.

Heat of solution and heat of reaction are important enthalpy values in physical chemistry which are useful in the determination of properties of solutions and chemical reactions.

CONTENTS

1. Overview and Key Difference
2. What is Heat of Solution 
3. What is Heat of Reaction
4. Heat of Solution vs Heat of Reaction in Tabular Form
5. Summary – Heat of Solution vs Heat of Reaction 

What is Heat of Solution?

Heat of solution or enthalpy of solution is the amount of heat energy released or absorbed by a chemical system upon formation of a solution. This enthalpy value is related to the dissolution of a substance in a solvent that is in constant pressure, which results in an infinite dilution.

Most often, the heat of solution is given for a constant temperature in KJ/mol. There are three parts of this energy change: endothermic break down of chemical bonds that exist in the solvent, break down of chemical bonds within the solute, and the formation of attraction forces between the solute and the solvent. Moreover, we can say that an ideal solution usually contains a null enthalpy of mixing while a non-ideal solution has an excess molar quantity.

When considering most gases, the dissolution is exothermic. When a gas is dissolving in a liquid, energy is released as heat by warming both the solution and the surroundings. The temperature of the solution tends to decrease eventually, matching the temperature of the surrounding. Further, if we heat a saturated solution of a gas, the gas tends to come out of the solution.

What is Heat of Reaction?

The heat of reaction or reaction enthalpy is the difference between total reactant and total product molar enthalpies that are calculated for chemical substances in the standard state. This enthalpy value is useful in predicting the total chemical bond energy that is released or bound during the chemical reaction. Here, we need to account for the enthalpy of mixing as well.

In the determination of the heat of reaction, the standard state can be defined for any temperature and pressure value, and the value must be specified for that particular temperature and pressure, but the values are typically given at 25 Celsius degrees temperature and 1 atm pressure.

When considering the ions in an aqueous solution, we can choose the standard state, considering that the aqueous H+ ion concentration of exactly 1 mol/L has a zero standard enthalpy of formation. This makes it possible to tabulate the standard enthalpies for cations and anions at a similar standard concentration.

What is the Difference Between Heat of Solution and Heat of Reaction?

The heat of solution and heat of reaction are important enthalpy values in physical chemistry which are useful in the determination of properties of solutions and chemical reactions. The key difference between heat of solution and heat of reaction is that heat of solution is the amount of heat energy released or absorbed by a chemical system upon formation of a solution, whereas heat of reaction is the difference between total reactant and total product molar enthalpies that are calculated for chemical substances in the standard state.

The below infographic lists the differences between heat of solution and heat of reaction in tabular form for side by side comparison.

Summary – Heat of Solution vs Heat of Reaction

Heat of solution and heat of reaction are important enthalpy values in physical chemistry which are useful in the determination of properties of solutions and chemical reactions. The key difference between heat of solution and heat of reaction is that heat of solution is the amount of heat energy released or absorbed by a chemical system upon formation of a solution, whereas heat of reaction is the difference between total reactant and total product molar enthalpies that are calculated for chemical substances in the standard state.