Chem Test #3

Question 1

How is it possible for liquids to evaporate at temperatures below their boiling point under standard pressure?

Answer 1

• Boiling is rapid evaporation of a liquid
• This happens because there are small amounts of particles in a substance that have the KE to break free of its IMF and can change state
• Using a Boltzmann distribution graph, we would see that there are small amounts of particles that have the KE similar to that of a “boiling” substance

Question 2

5 points of the KMT

Answer 2

• The has consists of objects with a defined mass and zero volume
• The gas particles travel randomly in a straight line motion where their movement can be described by the fundamental laws of mechanics
• All collisions involving gas particles are elastic; the KE of the system is conserved even thought the KE among the particles is redistributed
• The gas particles do not interact with each other or with the walls of any container
• The gas phase system will have an average KE that is proportional to temperature; the KE will be distributed among the particles according to a Boltzmann type of distribution

Question 3

What does the Maxwell Boltzmann distribution curve represent?

Answer 3

• The range if PE at a given temperature

- It shows the # of particles per KE

Question 4

What’s the difference between a “normal” cube and a Boltzmann curve?

Answer 4

• Normal curve is symmetrical and bell shaped

- Boltzmann is asymmetrical and skewed to the right

Question 5

KE

Answer 5

• is based on the motion of an object

- relates to temperature

Question 6

PE

Answer 6

• is based on the postition of state of matter
• this energy relates to a substance state
• depends on IMF acting on a substance

Question 7

What is occuring with regard to KE and PE on a heating graph?

Answer 7

• As heat energy is added, the temperature of a substance rises
• As the slope rises, KE is increasing in proportion to its temperature, which causes the particles to move more rapidly
• The point where plateaus a phase, change occurs where particles are breaking free from IMF and changes PE. More heat, the faster IMF are brocken and PE is changed

Question 8

Why doesnt the temperature of a boiling substance increase with the increased heat energy put into it?

Answer 8

• When a substance reaches its boiling point, its temperature no longer increases even as more heat is added to it
• This is because the particles that have reached the max boiling point are breaking free from IMF and changing state

Question 9

Conservation of energy

Answer 9

A law stating that energy is an isolated system that can neither be creater nor destroyed
- it can only change its form

Question 10

Flow of heat

Answer 10

• Endothermic reactions cause the surroundings to cool and the reactant to heat
• Exothermic reactions cause the surroundings to heat up and the reactant to cool.

Question 11

Explain endo and exothermic processes

Answer 11

• Endothermic processes require utilization of heat energy and exothermic processes give off energy
• These processes are related to the conservation of energy in ordet to distribute KE in a system

Question 12

Solid

Answer 12

• Particles are tightly packed
• Object will hold its shape
• Contains lots of negative potential energy
• Motion is limited to vibrational

Question 13

Liquid

Answer 13

• can change shape
• motion of particles contain a bit of translational, rotational and vibrational
• flows and conforms to the walls of its container

Question 14

Gas

Answer 14

• motion of particles are random (mostly translational)
• has no definite shape or volume
• mostly KE, no PE
• least dense state

Question 15

How can the KMT be used to describe the effect of heat on the volume of solids and liquids?

Answer 15

• the gas phase system will have an average KE that is proportional to temperature
• therefore, the higher the temperature, the higher the KE there is within the solid/liquid
• more KE requires more space for particles to move in and then the volume of the liquids/solids will expand

Question 16

How does KMT explain why the cooling of a gas result in less gas pressure?

Answer 16

• since avg. KE is proportional to temperature, and cooling causes the temperature to drop, there is less KE within the gas
• if there was less KE, it causes most of the particles to slow down and take up less space
• if they take up less space within a volume, the pressure is less

Question 17

How does the Galileo thermometer work?

Answer 17

• less dense objects float on more dense objects
• density is inversely proportional to volume
• the Galileo thermometer is read by reading the temperature off the lowest floating density calibrated bulb
• when the liquid warms up it becomes less dense and fewer density calibrated bulbs can float in it
• volume up, density down. When the liquid warms up it’s density goes down
• when liquids increase in temperature their avg. KE goes up as well as the velocity of the liquid particles causing the volume to increase

Question 18

How does the drinking bird work

Answer 18

• the liquid on head of the bird will evaporate
• since all collisions are elastic, the KE system is conserved, therefore evaporation takes KE for the particles to evaporate
• the particles in the hollow head slow down because KE is proportional to its temperature
• when the particles slow down, they take up less space and the pressure of the gas will decrease
• the pressure in the bottom tube remains constant while the top is less than the bottom
• the shift in weight causes the bird to tilt and the pressure equalizes causing it to repeat

Question 19

How can the boiling point of a liquid be changed without the application or removal of heat?

Answer 19

• boiling point is about the matching of KE of the liquid with KE needed to break IMF and overcome the resistance of the atmospheric pressures above it
• if we were able to lower the atmospheric pressure of the air above the liquid, we would be able to lower the boiling point