Home / iGCSE Chemistry 0620 Extended – 6.1 Physical and chemical changes- Exam Style Questions Paper 4
A list of chemical and physical processes, A to H, is shown.
A combustion
B diffusion
C melting
D neutralisation
E photosynthesis
F reversible reaction
G roasting
H thermal decomposition
Answer the following questions about processes A to H.
Each letter may be used once, more than once or not at all.
(a) State which of the processes A to H happens when an acid reacts with an alkali.
(b) State which of the processes A to H reaches a position of equilibrium.
(c) State which of the processes A to H involves particles changing from fixed positions to being mobile, but still touching.
(d) State which two of the processes A to H are physical changes.
(e) State which of the processes A to H is caused by gas particles colliding with each other.
Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):
• Topic 7.1 — The characteristic properties of acids and bases (Part (a))
• Topic 6.3 — Reversible reactions and equilibrium (Part (b))
• Topic 1.1 — Solids, liquids and gases (Part (c))
• Topic 6.1 — Physical and chemical changes (Part (d))
• Topic 1.2 — Diffusion (Part (e))
(a) D (neutralisation)
Neutralisation is the specific reaction between an acid and an alkali (base), producing a salt and water. The H⁺ ions from the acid react with OH⁻ ions from the alkali.
(b) F (reversible reaction)
A reversible reaction in a closed system reaches dynamic equilibrium. At this point, the forward and reverse reactions occur at equal rates, so the concentrations of reactants and products remain constant.
(c) C (melting)
Melting is a physical change of state. In a solid, particles vibrate around fixed positions, but when melted, they gain enough energy to slide past each other (become mobile) while still remaining in contact as a liquid.
(d) B (diffusion) and C (melting)
Physical changes alter the form or state of a substance without changing its chemical composition. Diffusion is particle movement, and melting is a state change; neither creates new chemical substances.
(e) B (diffusion)
Diffusion in gases is driven by the random motion and frequent collisions of gas particles. These collisions cause particles to spread out from areas of high concentration to low concentration.