States of matter and particle modelIB MYP Sciences: Mind map

Exam questions on States of matter and particle model

1. At a school science fair in Dubai, a student shows a block of dry ice (solid carbon dioxide) in a bowl. The block gets smaller and a cold gas pours over the edge of the bowl, but no liquid collects in the bowl. The student explains the demonstration using the particle model, in which each particle is drawn as a small solid sphere.
   Explain, using the particle model, why a gas can be compressed into a smaller volume but a solid cannot.2 marks
2. In Dubai in summer, wet laundry hung on a balcony dries within a couple of hours, even though the temperature is far below 100 °C and the water never boils. A student wants to explain why the water leaves the clothes and why the air near the laundry feels slightly cooler.
   Explain, in terms of particles, why evaporation makes the remaining liquid cooler.2 marks
3. A student heats a solid sample of pure stearic acid in a water bath and records its temperature every minute. The temperature rises steadily from 20 °C, stays at 69 °C for several minutes while the solid melts, and then rises again.
   State the melting point of stearic acid and explain, in terms of particles and energy, why the temperature stays constant while it melts.3 marks