Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Energy changes in chemical reactions occur because energy is required to break chemical bonds in reactants and is released when new bonds are formed in products.
An Exothermic Reaction is a chemical change in which heat is released to the surroundings. The temperature of the surroundings increases. Example: Burning of coal ().
An Endothermic Reaction is a chemical change in which heat is absorbed from the surroundings. The temperature of the surroundings decreases. Example: Decomposition of Calcium Carbonate ().
Respiration is a vital exothermic process where glucose reacts with oxygen to release energy: .
Photosynthesis is a natural endothermic process where plants absorb solar energy to produce food: .
The physical state change of dissolving certain salts, like in water, absorbs heat, while dissolving in water releases heat.
📐Formulae
💡Examples
Problem 1:
When Nitrogen () and Oxygen () are heated to a very high temperature, they form Nitric Oxide (). Is this an exothermic or endothermic reaction?
Solution:
Endothermic Reaction.
Explanation:
The reaction requires a large amount of heat energy to be absorbed to break the strong bonds in and molecules. The equation is represented as: .
Problem 2:
Slaking of lime involves adding water to Quicklime (). Describe the energy change observed.
Solution:
The reaction is highly Exothermic.
Explanation:
When water is added to , it reacts vigorously to form Slaked Lime () and releases a large amount of heat energy, often causing the water to boil. .
Problem 3:
Categorize the process of 'Burning of Natural Gas' () based on energy change.
Solution:
Exothermic Reaction.
Explanation:
Combustion reactions, like the burning of methane (), always release energy in the form of heat and light to the surroundings. .