Endothermic reaction

• Endothermic reaction describes a process which absorbs thermal (heat) energy.
• ∆H = positive
• Products contain more energy than the reactants. E₂ > E₁
• Heat energy is absorbed from the surroundings and is converted to chemical energy during the reaction. This increases the energy contents of the products.
• Total heat energy given out during the formation of chemical bonds < Total heat energy absorbed during the breaking of chemical bonds.
• Temperature of the surroundings decreases i.e. the reacting mixture becomes cold. 

Exothermic reaction

• Exothermic reaction: a chemical reaction that produces heat.
• ∆H = negative
• Reactants contain more energy than the products. E₁ > E₂
• Chemical energy decreases during the reaction and is converted to heat energy (heat is given out).
• Total heat energy given out during the formation of chemical bonds > Total heat energy absorbed during the breaking of chemical bonds.
• Temperature of the surroundings increases i.e. the reacting mixture becomes hot.  

SPM Form 5: Thermochemistry (Checklist)

• Thermochemistry is the scientific study of heat that is released or absorbed during chemical changes.
• Exothermic reaction: A chemical reaction that involves liberation of heat to the surroundings. The increase in the temperature of the reacting mixture indicates an exothermic reaction.
• Endothermic reaction:  A chemical reaction that involves absorption of heat from the. The decrease in the temperature of the reacting mixture indicates an endothermic reaction.
• Heat of precipitation: The change in heat energy when one mole of a precipitate is formed from their ions in aqueous solutions.
• Heat of displacement: The change in heat energy when one mole of a metal is displaced from its salt solution by a more electropositive metal.
• The higher the position of the more electropositive metal is in the electrochemical series, the bigger the value of heat displacement of copper by the metal.
• Heat of neutralization: The change in heat energy when one mole of water is formed from the neutralization of an acid and an alkali.
• Heat of neutralization for reaction between any strong acid and any strong alkali is a constant.
• The values of heat neutralization for reactions between strong acids and strong alkalis are higher than that of reactions between strong acids and weak alkalis, weak acids and strong alkalis or weak acids and weak alkalis. 
• Heat of combustion: The change in heat energy when one mole of substance is completely combusted in excess oxygen under standard conditions.
• The greater the number of carbon atoms per molecule of an alcohol, the greater the value of heat of combustion of the alcohol.

SPM Chemistry Syllabus Form 5

Chapter 1: Rate of reaction

1.1 Rate of reaction

1.2 Factors affecting the rate of reaction

1.3 Collision theory

Chapter 2: Carbon Compounds

2.1 Carbon compounds

2.2 Alkanes

2.3 Alkenes

2.4 Isomerism

2.5 Alcohols

2.6 Carboxylic Acids

2.7 Esters

2.8 Fats

2.9 Natural rubber

Chapter 3: Oxidation and Reduction

3.1 Redox reactions

3.2 Rusting as a redox reaction

3.3 The reactivity series of metals and its application

3.4 Redox reactions in electrolytic and chemical cells

Chapter 4: Thermochemistry

4.1 Energy changes in chemical reactions

4.2 Heat of precipitation

4.3 Heat of displacement

4.4 Heat of neutralization

4.5 Heat of combustion

4.6 The existence of various energy sources

Chapter 5: Chemical for Consumers

5.1 Soap and detergent

5.2 Food additives

5.3 Medicines

5.4 The existence of chemicals