IGCSE CHEMISTRY REVISION [Syllabus 7]- Chemical Reactions

Summary

This IGCSE Chemistry revision video covers key concepts in chemical reactions, including the difference between chemical and physical changes, collision theory, and factors affecting reaction rates such as concentration, temperature, pressure, and particle size. It also explains reversible reactions and equilibrium, emphasizing how changes in conditions shift the position of equilibrium. The video introduces catalysts and their role in reactions, and concludes with an overview of redox reactions, explaining oxidation and reduction in terms of oxygen and electron transfer. The content is designed to aid exam preparation.

Takeaways

• 🔍 Chemical reactions differ from physical changes, where a physical change involves state changes like ice to water, while chemical changes occur at a molecular level.
• ⚡ The collision theory explains that for a chemical reaction to happen, particles must collide and have sufficient energy for the reaction to proceed.
• 🌡️ The rate of chemical reactions is influenced by factors like concentration, pressure, temperature, and particle size, each affecting collision rates and energy levels.
• 🔬 Higher concentration increases collision rates due to more particles being closer together, speeding up the reaction.
• 💨 Pressure affects gases by increasing particle collisions in a confined space, leading to faster chemical reactions.
• 🔥 Temperature impacts reaction rates by increasing particle energy and speed, leading to more frequent and forceful collisions.
• 🧊 Smaller particle sizes provide larger surface areas for collisions, which enhances reaction speed, especially in solids.
• 🔗 Catalysts, such as enzymes, speed up chemical reactions without being consumed, affecting both forward and reverse reactions without altering the reaction equilibrium.
• ⚖️ Equilibrium in reversible reactions occurs when the rate of the forward reaction equals the rate of the reverse reaction, stabilizing the concentrations of reactants and products.
• 🔄 Changes in conditions like concentration, temperature, and pressure can shift the equilibrium, favoring either the forward or reverse reaction depending on the situation.

Q & A

What is the difference between a chemical change and a physical change?

A chemical change occurs at a molecular level when two or more molecules interact and form new substances, while a physical change involves changes in the state of matter without altering the chemical structure, such as ice turning into water.

What are the two key conditions for a chemical reaction to occur according to the collision theory?

The two conditions are: 1) particles must collide, and 2) they must have sufficient energy during the collision for the reaction to occur.

How does concentration affect the rate of a chemical reaction?

Higher concentration increases the number of particles in a given volume, leading to more frequent collisions, which increases the rate of the chemical reaction.

What is the effect of pressure on the rate of chemical reactions involving gases?

Higher pressure increases the number of gas particles in a given space, leading to more collisions and an increased rate of reaction. Pressure only affects reactions involving gases.

How does temperature affect the rate of a chemical reaction?

Higher temperature increases the energy and speed of particles, leading to more frequent collisions and higher energy, thus increasing the rate of reaction.

Why does smaller particle size increase the rate of chemical reactions in solids?

Smaller particle size increases the surface area available for collisions, allowing more particles to react simultaneously, thus increasing the rate of the chemical reaction.

What is the role of catalysts in chemical reactions?

Catalysts speed up chemical reactions without being consumed in the process. They do this by lowering the activation energy required for the reaction to occur.

What is a reversible reaction, and what happens at equilibrium?

A reversible reaction is when the products of a reaction can react to form the original reactants. At equilibrium, the forward and reverse reactions occur at the same rate, so the concentrations of reactants and products remain constant.

How does the position of equilibrium shift when the concentration of reactants or products is changed?

If the concentration of reactants increases, the equilibrium shifts to the right, producing more products. If the concentration of products increases, the equilibrium shifts to the left, producing more reactants.

What is a redox reaction, and how can it be defined in two ways?

A redox reaction involves both reduction and oxidation. It can be defined by oxygen transfer (oxidation is the gain of oxygen, reduction is the loss of oxygen) or by electron transfer (oxidation is the loss of electrons, reduction is the gain of electrons).