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Flashcards in THERMO5 Deck (24):
1

How can you raise the temperature of a system?

-adding heat
-doing work on it

2

One Joule
Definition

-the mechanical (potential) energy required to raise the temperature of 1g of water by 1K

3

First Law of Thermodynamics

ΔEint = Qin + Won

ΔEint = increase in internal energy of the system
Qin = heat transferred into the system
Won = work done on the system

4

cv'

molar specific heat at a constant volume

5

cp'

molar specific heat at constant pressure

6

Ratio Between cv' and cp' as

cp' > cv' for substances that expand on heating since work is done against the surroundings during expansion
cp' ≈ cv' for liquids and solids as any expansion is very small

7

Determining Won

-for a gas exerting a force F on a piston surface area A, the work done by the gas to move the piston a distance dx is
dWby = Fdx = PAdx = PdV
-the work done on the gas is the negative of the work done by the gas
-so dWon = -Pdv, giving

Won = -∫P dv

8

Won
Constant Pressure

Won = -PΔV

9

Won
Constant Volume

Won = 0

10

First Law of Thermodynamics
Ideal Gas at Constant Volume

ΔEint = CvΔT

11

First Law of Thermodynamics
Ideal Gas at Constant Pressure

ΔEint = CpΔT - PΔV

12

Mayer's Equation

Cp - Cv = nR
AND
cp' - cv' = R

13

Monatomic Gas
cv'

cv' ≈ 1.5R

14

Diatomic Gas
cv'

cv' ≈ 2.5R

15

Polyatomic Gas
cv'

cv' > 2.5R

16

How to find cv' for the general case

Cv = dEint/dT
and cv' = Cv / n

17

What does internal energy in an ideal gas depend on?

only temperature

18

Joule Thompson Effect
Definition

a real gas cools when undergoing a free expansion

19

Joule Thompson Effect
Expansion of Ideal Gas into Vacuum

-gas allowed to freely expand into the vacuum in apparatus insulated from the surroundings
-when the gas reaches equilibrium the temperature is found to have remained for constant (for gases at low density)
-shows that internal energy does not depend on the volume of a ideal gas
KEav = 3/2 nRT

20

Joule Thompson Effect
Expansion of Real Gas into Vacuum

-real gases have attractions between molecules
-as the gas expands, the potential energy of the molecules is increased as they get further apart
-for a rigid insulated system this increase in PE can only come from reducing the KE
-so the temperature is reduced slightly

21

Heat Capacity Ratio
Equation

γ = Cp / Cv = cv' / cp'

22

Monatomic Gas
Heat Capacity Ratio

γ = 5/3 ≈ 1.67

23

Diatomic Gas
Heat Capacity Ratio

γ = 7/5 ≈ 1.40

24

Polyatomic Gas
Heat Capacity Ratio

γ = 8/6 ≈ 1.33