Chem quiz U. 7

Effect of adding or removing gas at constant volume

Adding gas increases the pressure; this is a direct relationship.

Effect of increasing or decreasing volume on gas pressure

Decreasing volume increases pressure; this is an indirect relationship.

Effect of raising or lowering temperature on gas pressure

Increasing temperature increases pressure; this is a direct relationship.

Why are gases easy to compress?

Gases have large spaces between particles, allowing them to be confined to smaller places.

How does compressing a gas from 4L to 1L affect pressure at constant temperature?

The pressure will quadruple (increase by a factor of 4).

What is the triple point in a phase diagram?

The point where all phases (solid, liquid, gas) are in equilibrium.

What is the ability of liquid and gas particles to slide past one another called?

Flow.

What are the forces that keep liquid particles together?

Intermolecular forces of attraction.

Do particles in the liquid state have greater or lesser IM attractive forces than in the gas state?

Greater IM attractive forces.

What term describes gases in response to pressure applied?

Gases are compressible.

What term describes liquids in response to pressure applied?

Liquids are slightly compressible.

What is the conversion of liquid to gas below boiling point called?

Evaporation.

Where does evaporation occur in the liquid?

At the surface of the liquid.

How does increasing temperature affect the rate of evaporation?

It increases the rate of evaporation.

Why is evaporation a cooling process?

Particles with the highest kinetic energy escape, leaving lower KE particles behind.

What state is a system in when 2 opposite reactions occur at the same rate?

Equilibrium.

When does equilibrium occur for a liquid in a closed container?

When the rate of evaporation equals the rate of condensation.

What does dynamic equilibrium mean?

Both reactions are still occurring.

What is evaporation?

A liquid converting to a gas below the substance’s boiling point.

What happens to temperature of a liquid due to evaporation?

Evaporation lowers the temperature of the liquid.

What is the difference in evaporation between contained and uncontained liquids?

Contained liquids reach equilibrium; uncontained liquids can diffuse and do not reach equilibrium.

Why does increasing temperature increase evaporation rate?

It increases kinetic energy, allowing particles to overcome intermolecular forces.

As the temperature of a liquid increases, the vapor pressure of the substance will? I

Increase

The temperature at which a substance actively changes from liquid to gas is called the?

Boiling Point

The condition necessary for a substance to boil is for the _____ _______of the liquid to equal the surrounding atmospheric pressure.

Vapor Pressure

The normal boiling point of a liquid is the temperature at which a substance boils when the atmospheric pressure is equal to?

101.3 kPa

The normal boiling point for water is equal to 100 °C which is equal to

373 K, the temperature at which water boils at 1 atmosphere of pressure.

Substances with weaker intermolecular (IM) forces will tend to have____ vapor pressure than substances with stronger IM forces.

High

Substances with weaker IM forces will tend to have _____ boiling points than substances with stronger IM forces.

Lower

In your own words, explain dynamic equilibrium.

Dynamic eq. occurs when reaction rates are equal in a closed system. It is called “dynamic”
because it may appear as if nothing is occurring, but the reactions are still happening on the
molecular level

What is vapor pressure?

The pressure caused by evaporated particles above a liquid.

Would you expect an equilibrium vapor pressure to be reached above a liquid in an open
container? Why or why not?

No – because without the lid the particles would diffuse out. (There would be no condensation.)

Describe the effect that increasing temperature has on the vapor pressure of a liquid.

Increasing the temperature of a liquid will increase the vapor pressure of the liquid because the
particles are able to break free of the IM forces more readily.

Describe the effect of intermolecular forces on the vapor pressure of a liquid.

If the IM forces of a liquid increase, the vapor pressure of the liquid will lower because these
particles are more attracted to each other. (Ex: water)

What is the difference between the B.P. and n.B.P. of a liquid?

The B.P. of a liquid can be observed anywhere. But the n.B.P. can only be observed at standard
pressure (sea level).

At the top of Mt. Everest, atmospheric pressure is much lower than at sea level. Would you
expect the water to boil at 100°C, less than 100°C, or greater than 100°C at the top of Mt.
Everest? Why?

The water would boil at less than 100. Since the atm pressure is lower it would take less vapor
pressure of the liquid to equal atm pressure. So a lower boiling point of the water would be
observed.

Describe what condition is necessary in order for a solid to melt.

The particles must be able to overcome the IM forces of attraction.

In order to sublime, the vapor pressure of the solid needs to equal the surrounding ___?

Atmospheric pressure.

The movement of solid particles can be described as ___?

Vibrating in place