chapter 20

Question 1

what assumptions break down for real gases?

Answer 1

• molecules are well separated

- molecules exert no force on each other

Question 2

what is the van der waals equation of state?

Answer 2

(P+an^2/V^2)(V-bn)=nRT

Question 3

why is the constant a needed in the van der waals equation?

Answer 3

as the molecule collides with the container wall, the molecule feels a stronger attraction from other molecules. this pulls the molecule away from the wall causing the change in momentum to be less. real pressure is lower than ideal

Question 4

why is the constant b needed in the van der waals equation?

Answer 4

• b=V*Na, the actual volume of one mole of gas molecules

- gas molecules have a finite size so the free volume available to each molecule is reduced.

Question 5

what is the coefficient of linear expansion equal to?

Answer 5

ΔL/LΔT

Question 6

what is the coefficient of volume expansion equal to?

Answer 6

ΔV/VΔT

Question 7

what are the assumptions of an ideal gas?

Answer 7

• gas contains many molecules
• molecules are well separated
• direction of molecules is random
• molecules exert no force on each other
• all collision are elastic

Question 8

define a saturated vapour

Answer 8

a saturated vapour is one in equilibrium with its liquid (horizontal lines on PV graph)

Question 9

what is the critical point on a PV or PT graph?

Answer 9

when the densities of vapour and liquid are equal so they are no longer indistinguishable. at temperatures greater than the critical point, the gas will not condense at any given temp.

Question 10

what is the triple point?

Answer 10

when solid, liquid and vapour are all in equilibrium

Question 11

why is the PT diagram different for water compared to other substances?

Answer 11

• water expands on freezing when cooled, so the line TB has a negative slope for water rather than a positive slope for other substances.
• melting temperature decreases with higher pressures

Question 12

what is the relative humidity equation?

Answer 12

RH = (partial pressure of H20/saturation vapour pressure of H20) x 100

Question 13

what is temperature gradient?

Answer 13

the change of temp (for example along a bar) = dT/dx

Question 14

what is thermal current?

Answer 14

I = dQ/dt = -kAdT/dx

units is Watts

Question 15

what are the thermal rules for in series?

Answer 15

• I1 = I2 = I3

- Rtotal = R1 + R2

Question 16

what are the thermal rules for in parallel?

Answer 16

• Itotal = I1 + I2
• Itotal = ΔT/Rtotal
• 1/Rtotal = 1/R1 + 1/R2

Question 17

what is the stefan boltzmann law?

Answer 17

P = eσAT

and Pnet = eσA(T^4 - To^4)