CHAPTER 5 | thermochemistry
Heat Change in Chemical Reactions
Heat or energy change occurs in most of the chemical reactions.
When a chemical reaction occurs, heat is absorbed or released.
Heat is absorbed to break the bond in a compound. Conversely, heat is released when the bond is formed.
Chemical reactions can be classified into two types, i.e., exothermic and endothermic reactions.
The chemical reactions are applied in the making of hot and cold packs.
Exothermic Reaction
A reaction that releases heat to the surroundings.
When this reaction occurs, the reactant will lose heat to the surroundings.
Since heat is released from the reactant to the surroundings, the surrounding temperature is raised.
The contents in the container become hot. As a result, the container also feels hot when touched or shows a higher temperature when measured with a thermometer.
The total energy content of the product is less than the total energy content of the reactants.
(a) Burning of paper
(b) Reaction between sodium and water
Examples of exothermic reactions:
(c) Explosion of bomb
Endothermic Reaction
A reaction that absorbs heat from the surroundings.
When this reaction occurs, the reactant will gain heat from the surroundings.
Since heat is absorbed by the reactant from the surroundings, the surrounding temperature is lowered.
The contents in the container become cool. As a result, the container also feels cool when touched or shows a lower temperature when measured with a thermometer.
The total energy content of the product is more than the total energy content of the reactant.
Examples of endothermic reactions:
(a) Photosynthesis
(b) Baking cakes
(c) Dissolving ammonium nitrate powder in water
(b) Baking cake
(c) Dissolving ammonium nitrate powder in water
(a) Photosynthesis