Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
A chemical change is a permanent change in which the chemical composition of a substance is altered and one or more new substances are formed. For example: .
Close Contact: Some chemical reactions occur only when the reactants are brought into close contact in their solid state, such as iodine and phosphorus reacting spontaneously.
Solution Form: Certain substances react only when they are in a solution state (aqueous). For example, reacts with to form a precipitate of .
Heat: Many reactions require the supply of heat energy to initiate. These are often thermal decomposition reactions, such as .
Light (Photochemical Reactions): Some reactions take place only in the presence of light. A primary example is photosynthesis: .
Electricity (Electrochemical Reactions): Certain compounds decompose when an electric current is passed through them in a liquid or molten state, such as the electrolysis of water: .
Pressure: High pressure is required for certain gaseous reactions, such as the synthesis of ammonia where and react at high pressure.
Catalysts: Substances that increase or decrease the rate of a chemical reaction without undergoing any permanent chemical change themselves. For example, acts as a catalyst in the decomposition of .
📐Formulae
💡Examples
Problem 1:
What happens when and solutions are mixed? Name the condition required.
Solution:
Explanation:
This is a precipitation reaction. The condition required is that the reactants must be in their 'Solution state' (Aqueous) for the ions to move freely and react.
Problem 2:
Identify the catalyst used in the manufacture of ammonia by Haber's process and the necessary pressure condition.
Solution:
Catalyst: Iron (); Promoter: Molybdenum (); Pressure: Above atmospheres.
Explanation:
In Haber's process (), the reaction is reversible and requires high pressure and a catalyst to increase the yield and speed of ammonia production.
Problem 3:
Explain why silver nitrate is stored in dark-colored bottles.
Solution:
Explanation:
Silver nitrate is photosensitive. In the presence of light, it undergoes a photochemical decomposition. To prevent this chemical change, it is stored in dark bottles that block light.