11. Work and heat for gases

Question 1

What is means by the root mean squared velocity?

Answer 1

Measure of the speed of particles in a gas, defined as the square root of the average velocity-squared

Question 2

When an external force compresses the gas why is W= -p∆V and not W=p∆V

Answer 2

• when external force compresses the gas, work is done ON the gas (work should be positive)
• since volume is decreased, ∆V is negative
• to get a positive work, there needs to be a negative sign since, pos x pos = neg

Question 3

Describe the volume changes when work is done on a gas

Answer 3

• w > 0
• initial Volume > final volume
• gas compression

Question 4

Describe the volume changes when work is done by the gas

Answer 4

• w < 0
• initial volume < final volume
• gas expansion

Question 5

How to find the absolute value of work in a p-V diagram

Answer 5

Area under the curve = value of wokr

Question 6

What is the change in thermal energy of a system

Answer 6

• The heat flowing into a system

Q = ∆E thermal = (∆E thermal final) - (∆E thermal initial)

Question 7

What is the first law of thermodynamics

Answer 7

Conservation of energy
• the sum of all energy forms in an isolated system is constant
• the sum of all energy forms, in a close system, changes by the amounts of heat and work that flow between system and environment

Question 8

What are the four different types of thermodynamic processes?

Answer 8

• isochoric - constant volume
• isothermal - constant temperature
• isobaric - constant pressure
• adiabatic - constant heat

Question 9

Describe what happens in an isochoric system

Answer 9

• constant volume
• heat is supplied to the system from a hotter source
• work done on the system is zero
• internal energy increases with the temperature

Question 10

describe what happens in an isothermal process

Answer 10

• Heat Q is absorbed by the gas from a heat reservoir (which is same temp as the system)
• the internal energy is constant (bc temp is constant)
• the absorbed heat does work

Question 11

Describe what happens in an isobaric process

Answer 11

• constant pressure
• added heat increases the temperature
• internal energy and the gas increases
• Gas does work during the expansion

Question 12

Describe what happens in an adiabatic process

Answer 12

• all heat reservoirs are disconnected from the system
• no heat flow
• adiabatic expansion arises from internal energy of the system resulting in a change in temperature