Chemical and Physical Changes
List two signs that a chemical reaction has occurred.
Any of the following:
A colour change, gas production (bubbling/fizzing), formation of a precipitate, light/heat forming, temperature change.
What is the difference between intrusive and extrusive igneous rocks?
Intrusive igneous rocks form below Earth’s surface from slowly cooling magma and contain large/coarse crystals. Extrusive igneous rocks form above surface from rapidly cooling lava and contain fine-grained or glassy textures, often small or no crystals.
Name two types of potential energy.
Any of the following:
Gravitational potential energy, Elastic potential energy, Chemical energy, nuclear energy.
What is an independent variable?
The variable that the experimenter changes intentionally to test its effect on the dependent variable.
What is weathering?
Weathering is the breaking down of rocks in place by physical, chemical, or biological processes.
What is a solute and solvent?
Solute: the substance that is dissolved (e.g., salt).
Solvent: the substance that does the dissolving (e.g., water).
What is erosion, and how is it different from deposition?
Erosion is the process by which particles are worn away and transported by wind, water, ice, or gravity. Deposition is the process where eroded material is dropped (deposited).
What is the law of conservation of energy?
Energy cannot be created or destroyed; it can only be transformed from one form to another or transferred between objects. The total energy of a closed system remains constant.
What is a controlled variable?
A variable kept constant during an experiment so it does not affect the dependent variable.
What is heat energy?
Heat energy (thermal energy) is the internal energy of a substance due to the motion of its particles.
Describe thermal expansion and contraction.
Thermal expansion: when a substance is heated its particles gain kinetic energy, move further apart on average, and the material expands (increases in size or volume).
Thermal contraction: cooling reduces particle motion, particles move closer together, and the material contracts (decreases in size or volume).
Describe how metamorphic rocks are formed.
Metamorphic rocks form when existing rocks (igneous, sedimentary, or older metamorphic) are subjected to high pressure and/or high temperature (but not enough to melt them). This causes recrystallisation, new mineral growth, and texture changes while the rock remains solid.
Calculate the GPE of a 2 kg object lifted 3 m above the ground.
GPE = 58.8 J.
Identify the independent and dependent variables in an experiment measuring how temperature affects dissolving rate.
Independent variable (IV): temperature of the solvent (e.g., water).
Dependent variable (DV): dissolving rate (e.g., time taken for a fixed mass to dissolve or mass dissolved per minute).
Identify the energy transformations (all transformations useful and wasted) in a battery-powered torch.
Chemical energy (battery) → electrical energy (circuit) → useful: light energy from the bulb/LED.
Wasted: electrical energy → heat and a tiny amount of sound.
Identify whether rusting iron is a physical or chemical change.
It is a chemical change because iron and oxygen form iron oxide, which is a new product. This change is irreversible.
This rock shows distinct layers, contains rounded grains that are cemented together, and often breaks into flat sheets. What type of rock is it and why?
Clastic sedimentary rock. It shows distinct layers and it contains cemented grains.
Calculate the KE of a 4 kg object moving at 5 m/s.
50 J
Explain how to improve reliability in a student investigation.
Do multiple trials and average results; keep controlled variables constant; increase sample size; ensure consistent method.
A machine outputs 200 J of useful energy from 500 J of input energy. Calculate its efficiency as a percentage
Efficiency = 40%.
Explain why dissolving salt in water is sometimes considered both physical and chemical depending on context.
When salt dissolves in water, it forms a mixture, which can be reversible, so this can be considered a physical change.
Dissolving salt in water also causes the temperature to drop, which is a sign of a chemical change.
Compare regional, contact, and dynamic metamorphism.
Regional metamorphism occurs over large areas under high pressure and temperature. Contact metamorphism occurs where rock is heated by nearby magma or lava with little pressure change. Dynamic metamorphism occurs from high pressure.
Compare chemical potential energy and elastic potential energy in terms of where the energy is stored.
Chemical potential energy: stored in the bonds between atoms and molecules (e.g., fuels, food). Energy is released or absorbed when chemical bonds break/form.
Elastic potential energy: stored by deforming a material (stretching/compressing a spring, rubber band); energy is stored mechanically in the object’s shape and structure.
A student undertakes an experiment to test how different materials impact the temperature of water in a beaker.
What are the independent, dependent and two controlled variables in the experiment?
Independent variable: type of material (e.g., metal, wood, plastic).
Dependent variable: temperature change of the water (final temperature or temperature after a fixed time).
Two controlled variables: Any of the following: volume of water in each beaker; initial temperature of the water, same beaker size, same mass of material, same exposure time.
Explain why some reversible reactions still count as chemical changes even though products can turn back into reactants.
Reversibility doesn’t change the fact that bond breaking and bond formation occur. Chemical change means substances are transformed at the molecular level; reversible reactions still involve these chemical bond changes even if a reversible reaction allows conversion back to reactants.