Chemistry B L1 States of Matter

How are the temperature of a gas and the average kinetic energy of the particles of gas related?

• As the temperature of a gas increases, the average kinetic energy of the particles increases in direct proportion.

• As the temperature of a gas increases, the average kinetic energy of the particles increases exponentially.

• As the temperature of a gas increases, the average kinetic energy of the particles decreases.

• As the temperature of a gas increases, the average kinetic energy of the particles decreases exponentially.

Answer explanation

The average kinetic energy of the particles in a substance is directly related to the substance’s temperature.

 Which of the following are all assumptions of the kinetic theory as it regards gases?

• particles of gas are in constant motion, particles of matter are small spheres with an insignificant volume, particles of matter have mass

• particles of gas do not move, particles of matter have energy, particles of matter attract each other

• particles of gas are in constant motion, particles of matter are small spheres with an insignificant volume, collisions between particles of matter in gases are elastic.

• particles of gas are in constant motion, particles of matter exhibit repel each other, particles of matter have a definite volume

Answer explanation

Gases particles are in constant motion, atoms have mass, but insignificant volume, and because of the speed of gas particles and lack of attraction gas molecule collisions are elastic.

A closed container is partly filled with liquid.  A pressure sensor is in the gas space above the liquid.  If the gas pressure sensor reading does not change over a long period of time we can assume which of the following conditions are probably true?

•  

  No gas condensation is occurring.

•  

  No liquid evaporation is occurring.

•  

  There is no vapor in the container at all.

• The liquid and vapor are in dynamic equilibrium.

Answer explanation

In a system at constant vapor pressure, dynamic equilibrium exists. The rate of evaporation and the rate of condensation are the same.

According to the phase diagram for water, all of the following statements are true except

• an increase in pressure increases the boiling point

• it gives the conditions at which water exists as a solid, liquid, or gas

• a decrease in pressure lowers the melting point

• the normal melting point occurs at 0^oC

Answer explanation

A decrease in pressure increases the melting point.

Gas pressure results from what phenomenon?

• The volume of many small particles adding together to produce a large volume.

• The force of many small particles colliding with a surface.

• The weight of many small particles resting on a large surface.

• The energy of many small particles being lost over time as they collide with each other.

Answer explanation

Gas pressure is the result of billions of rapidly moving particles in a gas simultaneously colliding with an object.

The two crystalline forms of carbon, diamond and graphite, are best described as what?

• amorphous solids

•  

  allotropes

•  

  cubic crystals

•  

  ionic crystals

Answer explanation

Diamonds and graphite are allotropes because they are two different molecular forms of the same element.

Use the graph below to answer the following question. Which substance would boil at the highest temperature?

• Ethanol

• Water

• Chloroform

Answer explanation

A liquid boils when its vapor pressure equals the pressure of the atmosphere.  Since atmospheric pressure is 101.3 kPa, the chloroform will boil at about 60˚C, the ethanol will boil at about 75 ˚C, and the water will boil at about 100˚ C.

The boiling point of ethanol will be lowest _____. 

• the boiling point of ethanol does not change

• on a mountain top

• at a high barometric pressure.

• at the sea shore.

Answer explanation

Because atmospheric pressure is lower at higher altitude, boiling points decrease at higher altitudes like mountain tops. 

The transition from a solid directly to a gas is known as

• freezing

• vaporization

• condensation

• sublimation

Answer explanation

The change of state from a solid to gas is called sublimation.

The transition from a solid directly to a gas is known as _____________.

• freezing

• vaporization

• condensation

• sublimation

Answer explanation

The change of state from a solid to gas is called sublimation.