Physical and Chemical ChangesCambridge IGCSE Chemistry: Flashcards
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What is a physical change?
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- What is a physical change?
- A change in which no new substance is formed, such as a change of state.
- What is a chemical change?
- A change in which one or more new substances are formed as a result of a chemical reaction.
- Is melting ice a physical or chemical change? Why?
- Physical — it is still H2O, just in a different state; no new substance is formed.
- Is burning magnesium a physical or chemical change? Why?
- Chemical — magnesium oxide, a new substance with different properties, is formed.
- Which type of change is usually easier to reverse, physical or chemical?
- Physical changes are usually easily reversible; chemical changes are usually difficult or impossible to reverse.
- Name two practical methods for investigating the rate of a reaction.
- Measuring the change in mass of a reactant/product over time, and measuring the volume of gas formed over time.
- How would you measure the rate of a reaction that produces a gas, using mass?
- Place the reaction flask on a balance and record the decrease in mass over time as gas escapes.
- List the five factors that can change the rate of a reaction.
- Concentration of solutions, pressure of gases, surface area of solids, temperature, and the presence of a catalyst.
- What is a catalyst?
- A substance that increases the rate of a reaction and is chemically unchanged at the end of the reaction.
- Does a catalyst change the total amount of product formed in a reaction?
- No — it only changes how quickly the product forms, not the final amount.
- How does surface area affect rate of reaction?
- A larger surface area (smaller solid pieces) generally increases the rate of reaction.