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O-Level The Particulate Nature of Matter: worked solution
2 marks. Full working, one step per line.
Question
[Past-paper practical, O-level Chemistry, Paper 3] The water of crystallisation in anhydrous sodium carbonate can also be found using a two-stage equation: stage 1: Na2CO3(s) + 10H2O(l) -> Na2CO3(s) + 10H2O(g); stage 2: Na2CO3(s) + 10H2O(g) -> Na2CO3.10H2O(s). Using Kinetic Particle Theory, decide whether stage 1 takes in or gives out heat, and explain your reasoning. [2]
Worked answer
In stage 1 liquid water is converted to gaseous water (10H2O(l) -> 10H2O(g)). To change from a liquid to a gas, energy must be absorbed to overcome the forces of attraction between the water molecules and separate them. Therefore stage 1 takes in heat (it is endothermic).
Practise this topic
This question is part of O-Level The Particulate Nature of Matter, in O-Level Pure Chemistry.