Download ΔE=nC V ΔT

Thermodynamics &
Ideal Gases
Expression
Application
CV = 3R/2
Monatomic ideal gas
CV > 3R/2
Polyatomic ideal gas (found
experimentally)
CP=CV+R
All ideal gases
ΔH= ΔE+nRΔT
ΔE=nCVΔT
All ideal gases
ΔH=nCPΔT
All ideal gases
Thermodynamics & Ideal Gases
Thermodynamics Calorimetry
Molar heat capacity, heat required to raise
the temperature of one mole of the
substance 1 Kelvin.
Specific heat capacity, heat required to raise
the temperature of one gram of the
substance 1 Kelvin.
Or:
Specific Heat = Molar Heat/Molar Mass
Thermodynamics
ΔE = q + w; Δ H = qp therefore
Δ E = qP + w = Δ H + w
How much work would 0.0100
grams of nitrogen triiodide do
when it decomposed at STP?
2NI3(s)  N2(g) + 3I2(g)
Thermodynamics & Calorimetry
Suppose we drop a 100.0 gram piece of
iron at 200 oC into a large coffee cup
calorimeter containing 250 grams of water
at 25 oC. What will the final temperature be
inside the cup? The specific heats of iron
and water are 0.45 and 4.18 J-K-1-g-1.
If the density of the water changes from
0.993 to 0.985 g/ml will your answer
change? What are q, w, ΔE & Δ H for the
process?
Thermodynamics & Hess’s Law
For any reaction, Δ H is the same when going
from a particular set of reactants to a
particular set of products. The path followed
is irrelevant. E.g. (all gases except graphite)
CO + 1/2O2
Δ H2
C + O2
Δ H3
Δ H1
CO2
Δ H1 = Δ H2 + Δ H3 = (-110.5kJ)+(-283.0kJ)
Thermodynamics
Standard Enthalpies of Formation. ΔHfo:
The change in enthalpy during the formation
of 1 mole of a compound from the elements.
All substances are at their standard states.
gas
P = 1 atm
solution
1 M @ 1 atm
solid
pure solid
liquid
pure liquid
T
usually 25 oC
ΔHfo of any element in its SS is zero