Unit 1 Science

💗 Physical & Chemical Changes

Q: What is a physical change?
A: A change in physical appearance, no new substances form, chemical composition stays the same. It's reversible.

Q: What is a chemical change?
A: A change where a new substance forms, irreversible, and particles are rearranged.

Q: What are signs of a chemical change?
A: Bubbles, temperature change, colour change, sound, gas release, and original substance disappears.

💗 Types of Reactions

Q: What is a chemical synthesis reaction?
A: When two or more substances combine to form one product.
Example: A + B → AB (e.g. magnesium + oxygen → magnesium oxide)

Q: What is a chemical decomposition reaction?
A: When a compound breaks down into simpler substances.
Example: AB → A + B (e.g. water → hydrogen + oxygen)

💗 Understanding Reactions

Q: When do chemical reactions occur?
A: When bonds between atoms are broken and new bonds form.

Q: What is a reaction?
A: A rearrangement of atoms.

Q: What is reaction rate?
A: The speed at which a chemical reaction happens.

💗 Collision Theory

Q: What are the 3 principles of collision theory?
A:

1. Particles must collide to react.

2. Particles must have enough energy.

3. Particles must collide at the correct orientation.

💗 Factors Affecting Reaction Rate

Q: How does concentration affect reaction rate?
A: Higher concentration = faster reaction (more particles = more collisions).

Q: How does surface area affect reaction rate?
A: More surface area = faster reaction (more particles exposed).

Q: How does temperature affect reaction rate?
A: Higher temperature = faster reaction (more energy = more collisions).

Q: How does agitation affect reaction rate?
A: More agitation = faster reaction (increases energy and contact).

Q: What is a catalyst?
A: A substance that speeds up a reaction by lowering activation energy without being used up.

💗 Energy in Reactions

Q: What is an exothermic reaction?
A: A reaction that releases energy (usually heat or light). Temp increases.
Examples: Combustion, respiration.

Q: In an exothermic reaction, is the energy in reactants or products higher?
A: Reactants have more energy than products. Energy is released.

Q: What is an endothermic reaction?
A: A reaction that absorbs energy (from surroundings, as heat). Temp drops.
Examples: Photosynthesis, melting ice.

Q: In an endothermic reaction, is the energy in reactants or products higher?
A: Products have more energy than reactants. Energy is absorbed.

💗 Conservation of Mass

Q: What is the Law of Conservation of Mass?
A: Mass cannot be created or destroyed in physical or chemical changes.