iGCSE Physics (0625) 2.1.1 States of matter Paper 4 -Exam Style Questions- New Syllabus
Question
Liquids and gases are two states of matter.
(a) In both boiling and evaporation, a liquid changes into a gas.
(i) State two ways in which boiling differs from evaporation.
1.
2.
(ii) Before injecting a patient, a doctor wipes a small amount of a volatile liquid on to the patient’s skin.
Explain, in terms of molecules, how this procedure cools the patient’s skin.
(b) Gases can be compressed but liquids are incompressible.
Explain, in terms of molecules, why liquids are incompressible.
Answer/Explanation
Answer:
(a) (i) any two from:
occurs throughout the liquid OR bubbles formed
occurs at one temperature / boiling point
does not produce cooling OR unaffected by draught / surface area / humidity
(ii) (more) energetic molecules escape (from the liquid) OR molecules gain energy and escape OR molecules
overcome intermolecular forces / break bonds
average speed decreases OR molecules with less (kinetic) energy left behind
temperature of liquid decreases
(thermal) energy conducted / gained from skin / body OR (thermal) energy lost by skin / body
(b) molecules touching OR no space between molecules
large (repulsive / intermolecular) forces (when moved closer)