Handout 1

Question 1

Equation for Internal Energy

Answer 1

delta U= q + w

Question 2

Mechanical Work

Answer 2

F x ds

Question 3

Expansion against constant pressure

Answer 3

w=- definite integral Pex dV

Question 4

Free expansion ISOTHERMAL IRREVERSIBLE (using volume)

Answer 4

w= -definite integral (V2,V1) pexdV = =pexdeltaV

Question 5

Isothermal REVERSIBLE

Answer 5

w=-nRTdefinite integral (V2,V1)dV/V= -nRTln(V2/V1)

Question 6

HEAT, q equation in terms of irreversible expansion

Answer 6

=q-pex(V2-V1)

Question 7

What does the heat, q, equation lead to at constant volume?

Answer 7

delta U= qv

Question 8

What does the heat, q, equation lead to at constant pressure?

Answer 8

expression for enthalpy…
where H= U+ pv
delta H=qp

Question 9

What is a state function?

Answer 9

any quantity whose value is independent of its history

Question 10

What is delta U for perfect gas?

Answer 10

delta U=0

Question 11

What are units for heat capacity?

Answer 11

JK-1 (mol-1)

Question 12

Constant volume heat capacity (INTEGRAL)

Answer 12

Cv= (delta U/T )v where dpv = dU

Question 13

Constant pressure heat capacity (INTEGRAL)

Answer 13

Cp= (delta H/T)p where dpq= dH

Question 14

What is experimental method for measuring internal energy change?

Answer 14

bomb calorimeter. Constant volume. Leads to delta U=qv

Question 15

How do we get to calorimeter equation?

delta U reaction = Ccal delta T/n

Answer 15

heat of combustion warms calorimeter. T equalises. n moles of compound to delta T.

Question 16

How can you define heat capacity in terms of a ratio?

Answer 16

heat capacity= dq/dt

Question 17

How do you measure enthalpy change experimentally?

Answer 17

DSC…. Differential Scanning Calorimeter

Question 18

Describe what happens in DSC thermogram.

Answer 18

Cp= heat flow/heat rate
Excess heat to keep sample and reference at same T. 
C= qp, ex/ delta T
Know H=qp, ex
Therefore Cpex = delta H/ delta T

Question 19

What is standard molar reaction enthalpy?

Answer 19

Change in enthalpy when reactants are converted to products at 1 bar and a specified temperature.

Question 20

Why can we get enthalpy change from products and reactants?

Answer 20

Because enthalpy is a state function

Question 21

What is standard enthalpy of formation?

Answer 21

Change in enthalpy when a substance is formed from its elements in their reference states at 1 bar and a specified temperature.

Question 22

What is Kirchoff’s Law?

Answer 22

Hm(T2) = Hm(T1) + Cpm (T2-T1)
Also put in delta r Hm
Can get delta Cpm as you would get enthalpy change (products - reactants)

Question 23

What relationship does Kirchoff’s law make use of? And what does it assume?

Answer 23

Cp= delta H/ delta T

Cp independent of T