The particle model, melting and boiling in terms of forces between particles, predicting state from melting and boiling points, and the limitations of the model.
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1.Describe the arrangement of particles in a solid.
Packed closely together in a regular arrangement, vibrating about fixed positions.
2.Describe the arrangement of particles in a liquid.
Close together but randomly arranged, able to move past one another.
3.Describe the arrangement of particles in a gas.
Far apart, randomly arranged, moving quickly in all directions.
4.What determines the state of a substance at a given temperature?
The strength of the forces between its particles, which depends on the type of bonding and structure.
5.What happens to the forces between particles when a substance melts?
Enough energy is supplied to overcome some of the forces, so the particles can move past one another.
6.What is the name of the change from liquid to gas?
Boiling, or evaporating.
7.What is the name of the change from gas to liquid?
Condensing.
8.What is the name of the change from liquid to solid?
Freezing.
9.What is sublimation?
When a solid turns straight into a gas without becoming a liquid first.
10.Is a change of state a physical or chemical change?
A physical change. The particles themselves do not change, only their arrangement and energy.
11.What does a high melting point tell you about a substance?
That the forces between its particles are strong.
12.A substance melts at 801 C and boils at 1413 C. What state is it at 20 C?
Solid, because room temperature is well below its melting point.
13.A substance melts at -114 C and boils at 78 C. What state is it at 20 C?
Liquid, because 20 C is above the melting point and below the boiling point.
14.What state symbol is used for a gas?
(g)
15.Give two limitations of the simple particle model.
It shows particles as solid spheres with no forces between them, when in reality they are not solid, they are not always spherical, and the forces between them vary.
16.Why is energy needed to melt a solid?
To overcome the forces of attraction holding the particles in their fixed positions.
17.Why does the temperature stay constant while a substance melts?
The energy supplied is used to overcome the forces between particles rather than to raise their kinetic energy.
18.What happens to the mass of a substance when it changes state?
It stays the same. No particles are lost or gained.
19.Why does a gas fill its container?
The particles move rapidly and randomly in all directions with almost no forces between them.
20.Why can liquids be poured but solids cannot?
The particles in a liquid can move past each other, whereas those in a solid are held in fixed positions.
21.Which has a higher melting point, a substance with strong forces or weak forces between particles?
The one with strong forces, because more energy is required to separate the particles.
22.Why does ice float on water?
Water is unusual: its particles are arranged slightly further apart in the solid than the liquid, so ice is less dense.
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