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Which of the following is an example of an exothermic reaction?
Burning of coal
Photosynthesis
Evaporation of water
Melting of ice
Burning of coal
An exothermic reaction is a chemical process that releases energy in the form of heat or light to the surroundings. The burning of coal is a classic example of a combustion reaction where carbon reacts with oxygen to release significant heat.
An exothermic reaction is a chemical process that releases energy in the form of heat or light to the surroundings. The burning of coal is a classic example of a combustion reaction where carbon reacts with oxygen to release significant heat.
Think of a campfire; as you burn wood or coal, the energy stored within the fuel is 'unlocked' and released into the air as heat, keeping you warm.
EXO means 'Exit'тАФenergy exits the system.
C(s)+O2тАЛ(g)тЖТCO2тАЛ(g)+Heat тАФ Combustion of carbon (exothermic reaction)
╬ФH=HproductsтАЛтИТHreactantsтАЛ тАФ Enthalpy change formula where negative signifies heat release
In an exothermic reaction, the total enthalpy of the products is lower than the total enthalpy of the reactants (╬ФH<0). During the combustion of coal, the chemical bonds in the reactants are broken and new, more stable bonds are formed in the products, releasing the excess energy as thermal energy.
Exothermic reactions result in a temperature rise in the immediate surroundings.
Combustion, respiration, and neutralization reactions are typically exothermic.
Endothermic reactions require an input of heat to proceed, such as melting or photosynthesis.
Provides a source of energy for heating and electricity generation.
Combustion of coal releases greenhouse gases like CO2тАЛ contributing to global warming.
Power generation in thermal power plants.
Domestic heating and cooking.
Standard enthalpy change for burning carbon is approximately тИТ393.5┬аkJ/mol.
Option B (Photosynthesis) is endothermic, requiring solar energy. Option C (Evaporation) and Option D (Melting) are endothermic physical changes that require heat absorption from the surroundings.
A is correct тАФ Burning of coal is an exothermic reaction because it releases thermal energy into the environment through a combustion process.
Remember that 'Breaking bonds requires energy (endothermic)' while 'Making bonds releases energy (exothermic)'. In combustion, the energy released forming CO2тАЛ bonds is much greater than the energy required to break C and O2тАЛ bonds.
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