enthalpy

Question 1

how is enthalpy defines

how is enthalpy change measured

Answer 1

H = U + PV
is a state functions U P and V are also state function

dH = dU + d(PV)
= dU + PdV + VdP

Question 2

what is the enthalpy change equal to if constant pressure and volume

Answer 2

no gas produced
deltaV close to zero and pressure is constant dP=0
deltaH = deltaU
if no other work is done 
detlaH = q 
as deltaU= q + w

Question 3

what is deltaH at constant pressure

Answer 3

dH = dU + PdV
if only compression work done dU = dq - PdV
so
dH = dq - PdV + PdV
so dH = dq
So deltaH is the heat taken up by the system which contributes to changing the internal energy of the system and doing compression work

Question 4

which equation links dH and change in number of moles

Answer 4

dH = dU + dnRT

Question 5

what is the enthalpy change at constant volume

Answer 5

as dH = dU + dnRT
and dU = q + w and no compression work so constant volume dU = dq
dH = dq + dnRT

Question 6

what are the standard conditions

Answer 6

pressure = 1e5 pa
temp = 298.15 K

Question 7

what is heat capacity

Answer 7

lets us relate heat energy to temperature change

C = dq / dT

Question 8

what are types of heat capacity

Answer 8

SHC - (c, cp, cv) J/KgK heat energy to raise 1 kg of substance by 1 K

molar heat capacity - (Cm, Cp,m. Cv,m), J/molK heat energy to raise 1 mole of substance by 1 /k

heat capacity - (C, Cp, Cv) J/K heat energy to raise whole system by 1K

heat capacity of mixtures - where nx moles of each component with molar capacity Cmx : C = n1Cm1 + n2Cm2…..
or where mx kg of each component with SHC cx
C = m1c1 + m2c2 + …..