### Thermochemical Reaction A **chemical reaction which proceeds with the evolution or absorption of heat** is called a
Explanation level
This topic explains thermochemical reactions — chemical reactions that involve the evolution or absorption of heat — and introduces thermochemical equations.
Definition
Thermochemical Reaction
A chemical reaction which proceeds with the evolution or absorption of heat is called a thermochemical reaction.
Simple explanation: A thermochemical reaction is a chemical reaction that either releases heat or absorbs heat.
Thermochemical Equation
A balanced chemical equation which also shows the heat change of a chemical reaction is called a thermochemical equation.
Simple explanation: A thermochemical equation is a balanced chemical equation that includes the heat change (ΔH) as part of the equation.
Thermochemistry
The branch of chemistry which deals with the heat or thermal energy changes in chemical reactions is called thermochemistry.
Simple explanation: Thermochemistry is the study of heat changes in chemical reactions.
Main Idea
When a chemical change takes place, energy is exchanged between system and its surroundings.
Heat
Light
Work
etc.
A chemical reaction which proceeds with the evolution or absorption of heat is called a thermochemical reaction.
Simple explanation: In thermochemical reactions, heat is either given out or taken in.
Core Concept
Example of a Thermochemical Equation
C(s) + O2(g) → CO2(g) Δ H° = -393.5 kJ
Carbon (solid) reacts with oxygen (gas) to form carbon dioxide (gas).
393.5 kJ of heat is released (negative ΔH → exothermic).
Simple explanation: The equation shows both the chemical change and the heat change.
Two Types of Thermochemical Reactions
There are two types of thermochemical reactions:
Exothermic reactions — release heat
Endothermic reactions — absorb heat
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