# Solids, Liquids, and Gases Questions

## Bring on the tough stuff

1. Under what conditions is the ideal gas law most accurate? Under what conditions does the ideal gas law break down? Why?

2. What are the properties of a gas?

3. What are the main assumptions of the kinetic molecular theory of gases?

4. Explain the difference between evaporation below the boiling point of a liquid and evaporation at the boiling point of a liquid.

5. What is surface tension? How does it depend on intermolecular forces?

6. How do the melting points of molecular solids relate to those of other types of solids?

7. How does gas solubility depend on pressure? How does this relationship explain why a can of soda fizzes when it is opened?

8. Mary and Bob are both boiling water in different cities. If Mary's water boils at 86ºC and Bob's water boils at 90ºC which of the two is at a higher altitude? How do you know?

9. What is a colligative property? What were the four colligative properties discussed?

10. Explain, in words, the relationship between gas pressure and temperature. Also explain, in words, the relationship between gas pressure and volume.

1. Under what conditions is the ideal gas law most accurate? Under what conditions does the ideal gas law break down? Why?

The ideal gas law is most accurate when the volume of gas particles is small compared to the space between them (such as a small density). It is also accurate when the forces between particles are not important. The ideal gas law breaks down at high pressures and low temperatures. This breakdown occurs because the gases are no longer acting according to the kinetic molecular theory.

2. What are the properties of a gas?
The particles in gases are not in contact with each other and are free to move relative to one another. The spacing between individual particles is very far apart. A gas has no fixed volume or shape. It occupies both the shape and the volume of the container it occupies.

3. What are the main assumptions of the kinetic molecular theory of gases?
The kinetic molecular theory makes four main assumptions. The first is that the gas is a collection of molecules in constant motion. Secondly, there is no attraction or repulsion between the particles and collisions are perfectly elastic. Thirdly, there is a lot of space in between the particles relative to the particle size. Lastly, the speed of the particles increases with temperature.

4. Explain the difference between evaporation below the boiling point of a liquid and evaporation at the boiling point of a liquid.
Evaporation below the boiling point occurs because molecules on the surface of the liquid experience fewer attractions to the neighboring molecules and can therefore break away. At the boiling point, evaporation occurs faster because more of the molecules have sufficient energy to break away.

5. What is surface tension? How does it depend on intermolecular forces?
Surface tension is the tendency of liquids to minimize their surface area. Molecules at the surface have few neighbors to interact via intermolecular forces.

6. How do the melting points of molecular solids relate to those of other types of solids?
Molecular solids as a whole tend to have low to moderately low melting points relative to other types of solids. Strong molecular forces, however, can increase their melting points relative to each other.

7. How does gas solubility depend on pressure? How does this relationship explain why a can of soda fizzes when it is opened?
The solubility of gases increases with increases pressure. When a can of soda is opened, the pressure is lowered, decreasing the solubility of carbon dioxide. This causes bubbles of carbon dioxide to come out of solution.

8. Mary and Bob are both boiling water in different cities. If Mary's water boils at 86ºC and Bob's water boils at 90ºC which of the two is at a higher altitude? How do you know?
As altitude increases, atmospheric pressure decreases. As temperature increases, vapor pressure increases. Liquid boils when its vapor pressure exceeds atmospheric pressure. So because Mary's water boils at a lower temperature, she must be at a higher altitude, where atmospheric pressure is lower.

9. What is a colligative property? What were the four colligative properties discussed?
A colligative property is one that only depends on the number of solute particles not their identity. Freezing point depression, vapor pressure lowering, boiling point elevation, and osmotic pressure were all discussed.

10. Explain, in words, the relationship between gas pressure and temperature. Also explain, in words, the relationship between gas pressure and volume.
The relationship between gas pressure and temperature is a direct relationship. As the temperature of a gas (under constant volume) increases, the pressure also increases. The gas molecules are travelling at higher velocities and hit the walls of the container more often thereby increasing the pressure.

The relationship between gas pressure and volume is an inverse relationship. As the volume of a gas (under constant temperature), increases the pressure decreases. There is more room for the gas molecules to travel so they hit the container walls less often which means a lower pressure.