CHAPTER 5 | thermochemistry

• 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.

• 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 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