lecture 3

Question 1

under what condition is no work done in

Answer 1

under constant pressure

integral of v0 over v0 leading to an answer of 0

Question 2

what is tricky to measure in an isolated system

Answer 2

measuring change in volume

Question 3

what do we use to measure temp change

Answer 3

bomb calorimetry

Question 4

what conditions are met when we use an isolated container eith a fixed volume

Answer 4

work is 0 (bc integral of v0 - v0 gives 0 work)

change in internal energy = change in heat
change U = change q

Question 5

change in internal energy is given by

Answer 5

change in energy added as heat

change in work done TO the system

Question 6

so to measure the internal energy of a system in an isolated system we must

Answer 6

find change in temp

find change in volume

Question 7

in an isolated system, what is difficult to measure

Answer 7

change in volume

Question 8

what does a bomb calorimeter include

Answer 8

the sample
high pressure o2

Question 9

how do we measure the temp change in bomb calorimetry

Answer 9

ignite the sample
measure the temp of the water before and after ignition

Question 10

what is heat capacity

Answer 10

energy supplied as heat required to raise temp by a fixed amount

Question 11

equation for heat capacity

Answer 11

C = dq/dT

Question 12

equation for change in work done

Answer 12

w = Pext x change in volume

Question 13

equation for internal energy change at constant volume

Answer 13

U = q

Question 14

if U = q at constant volume,, how else can heat capacity be expressed

Answer 14

C = dU/dT

Question 15

what does the heat capacity at a constant volume tell us

Answer 15

tells us the internal energy needed to change the temp by a certain amount

C = dU/dT C=dq/dT

Question 16

heat capacity at constant volume equation and why we partially differentiate U

Answer 16

Cv = (dU/dT)v

we partially differentiate U as it may change with pressure

bc U = q w

and w = Pext vol

Question 17

kinetic energy of 1 particle

Answer 17

3/2 kBT

Question 18

kinetic energy of n moles of particles

Answer 18

3/2 nRT

Question 19

what is kB

Answer 19

R / avogadros

Question 20

equation for the molar heat capacity of a monatomic ideal gas at constant volume

Answer 20

3/2R

Question 21

what reaction conditions are needed in order to measure change in internal energy

Answer 21

no volume change

no heat change

Question 22

why do we find enthalpy change instead of change in internal energy

Answer 22

bc not many reaction undergo with constant volume and constant temp

its easier to measure enthalpy at standard reactions

Question 23

H equation // enthalpy equation

Answer 23

H = U +pV

Question 24

why is enthalpy easier to use than internal energy

Answer 24

in gas reactions, most reactions occur under constant prssure aka atmospheric pressure

which allows enthalpy change to equal change in q (heat supplied) 🔺H = 🔺q
under constant pressure

Question 25

if change in enthalpy = change in heat energy,,,, what else does it equal

Answer 25

change in internal energy + ( pressure x change in volume)
at constant pressure

Question 26

in a system where pressure is constant, how can we measure enthalpy

Answer 26

measure enthalpy change by measuring heat change

exo = – endo = +

Question 27

constant vol leads to

Answer 27

ZERO work done

Question 28

constant pressure leads to

Answer 28

finding enthalpy change by measuring heat change

(using a bomb calorimeter)

Question 29

enthalpy equation

Answer 29

H = U + pV

Question 30

molar enthalpy and molar internal energy in solids and liquids

Answer 30

practically identical

due to their small molar volume

Question 31

change in molar enthalpy and internal energy in gases ..

Answer 31

.. can be very different

Question 32

ideal gas enthalpy equations

Answer 32

H = U + pV
H = U + nRT

change H = change U + ngRT
ng = moles of gas

at constant temp: 3rd equation

Question 33

heat capacity at constant pressure

Answer 33

change H = change q (heat)

Cp = dq/dT =
Cp = (dH/dT)p

change in H = Cp x (change in temp)

Question 34

molar heat capacity
for a monatomic gas equation

Answer 34

Cp = 5/2R

Question 35

heat cap at constant vol

Answer 35

Cv = (dU/dT)v

Question 36

heat cap at constant pressure

Answer 36

Cp = (dH/dT)p

Question 37

in solids and liquids why is enthalpy so similar to internal energy

Answer 37

bc H = U + pV

but their change in volume is tiny tiny

so it can be written as H = U
molar enthalpy and molar internal energy is very similar due to such a small difference in molar volume

Question 38

in solids and liquids why is enthalpy so similar to internal energy

Answer 38

bc H = U + pV

but their change in volume is tiny tiny

so it can be written as H = U
molar enthalpy and molar internal energy is very similar due to such a small difference in molar volume

Question 39

in gases,, is the difference between molar enthalpy and molar internal energy large

Answer 39

yes!!!

H doesn’t equal U

Question 40

change in moles is positive if

Answer 40

moles increased

Question 41

change in moles is negative if

Answer 41

moles decreased

Question 42

when does U = q

Answer 42

when no work is done
when volume is constant

when volume doesnt change do to using a container with fixed volume

Question 43

bomb calorimetry is used to find what. and what conditions occur when using bomb calorimetry

Answer 43

measures ‘q’
however volume is constant and so
U = q

so bomb calorimetry shows us the change in internal energy