MOaD 5

Question 1

What conditions do chemists work in?

Answer 1

At constant (atmospheric) pressure and constant (room) temperature.

Question 2

is the internal energy useful for chemists?

Answer 2

the internal energyU(T,V) is inconvenient.

Question 3

what is the 1st LoTD formula

Answer 3

U = q + w

Question 4

calculating q from U,V,P

Answer 4

qp= (Uf+pVf) - (Ui+pVi)

Question 5

ΔH Formula

Answer 5

ormula= ΔU+pΔV

Question 6

relationship between heat and enthalpy

Answer 6

qp= Hf- Hi = ΔH

Question 7

what is the meaning of enthalphy?

Answer 7

state function that represents the heat change at constant pressure,qp.

Question 8

isobaric

Answer 8

constant pressure

Question 9

how to Measure Enthalpy

Answer 9

bomb calorimeter and converting U to H

Question 10

How to convert u to h if there is no pv work?

Answer 10

H=U

Question 11

How to convert u to h if there is pv work?

Answer 11

ΔH = ΔU + Δngas RT

Question 12

Why is ΔH = ΔU + Δngas RT equation unneeded for liquids and solids?

Answer 12

Solids or liquids take little volume compared to gases, so there are no pressure changes in the calorimeter.
ignore these in calculations of work done.

Question 14

(a) A bomb calorimeter increased in temperature from 20°C to 23°C when a voltage of 20 V drove a current of 18.57 A through a heater for 10 s. Calculate the heat capacity of the calorimeter.

Answer 14

The energy used, E = IVt = 3714 J; Hence, Ccal = E / ΔT = 3714 / 3 = 1238 J K-1

Question 15

This calorimeter then measured the heat of combustion from 0.7022 g of oxalic acid (C2H2O4) giving a temperature increase of 1.602°C. Calculate the molar internal energy of oxalic acid.

Answer 15

qV = U = CcalΔT = -1238 × 1.602 = -1984 J (Note: it’s –ve because heat is given out)

No. moles of oxalic acid,  n = 0.7022 / 90 = 0.00780 mol

       So,  ΔUm  = -1984 / 0.00780 = -254.4 kJ mol-1

Question 16

formula for U / qv

Answer 16

qV = U = CcalΔT

Question 17

Ccal formula

Answer 17

= E / ΔT

Question 18

cp heat capacity definition maths term

Answer 18

𝐶_𝑝=(𝜕𝐻/𝜕𝑇)_𝑝 at small t change and cp is constant

Question 19

definition of a heat capacity

Answer 19

‘the energy needed to raise the temperature of an object by 1 K’,

Question 20

cp heat capacity with large changes

Answer 20

ΔH=CpΔT and cp is constant

Question 21

what is the difference between cp and cv

Answer 21

the work done in pushing back the atmosphere, and

the work needed to stretch bonds in the material, including the weak (Van der Waals) interactions. The latter is zero for a perfect gas.

Question 22

is cp greater than cv?

Answer 22

Work has to be done withCp, the temperature rise will be less for a given heat transfer.

Cpis greater thanCV.

Question 23

relationship between cp and cv

Answer 23

cv + R = cp

Question 24

γ

Answer 24

=Cp/CV