thermo- chemistry. thermochemistry the study of heat transfer in chemical reactions
TRANSCRIPT
Thermo-chemistry
Thermochemistry
•The study of heat transfer in
chemical reactions
Thermo-chemical
Terms
Heat (H)•A form of energy
that can flow between samples of
matter
Heat cannot be measured directly; thus, we measure heat change (H)
Enthalpy Change•Heat that can flow in/out of a system
H
System•That part of nature upon which attention
is focused
Surroundings•That part of nature
which we are not focused
Reaction Coordinate
•A graph of energy change versus time in a chemical reaction
Time
Ene
rgy
RP
Exothermic Rxn•Chemical reactions
that release, give off heat, or lose
heat
Exothermic Rxn•Products will
contain less heat than the reactants
H < 0
Endothermic Rxn
•Chemical reactions that absorb, take in heat, or gain heat
Endothermic Rxn•Products will
contain more heat than the reactants
H > 0
Thermochemistry Topics
•Heat Change
•Calorimetry
•Thermochemical Equation
Topic: Heat
Change
Specific Heat•The heat required to raise one gram of a substance 1oC
•c: (J/goC, J/kgK)
Specific Heat Formula
H = mcT
Heat of Fusion•The heat required to melt one gram of a substance at its normal MP
•Hf: (J/g or J/kg)
Heat of Fusion Formula
H = mHf
Heat of Vaporization
•The heat required to boil one gram of a substance at its normal BP
•Hv: (J/g or J/kg)
Heat of Vap. Formula
H = mHv
Calculate the heat change when 10.0 g H2O goes from –100.0oC to 200oC.MP = 0oC BP = 100oCHf = 334 J/g HV = 2260 J/g
cice = 2.06 J/gKcwater = 4.18 J/gK csteam = 2.02 J/gK
Calculate the heat change when 5.00 g H2O goes from –10.0oC to 120oC.MP = 0oC BP = 100oCHf = 334 J/g HV = 2260 J/g
cice = 2.06 J/gKcwater = 4.18 J/gK csteam = 2.02 J/gK
Topic:
Calorimetry
Calorimetry•A study of how to
measure experimental heat
transfer in a system
Calorimeter•Device used to measure heat transfer
•A calorimeter is an adiabatic system
•Experimental yield
Adiabatic System•A system that exchanges zero heat with its surroundings
Hsystem = 0
H (J or kJ)H ~ q = the heat or enthalpy change in a system
Hsys = Hsys parts
CalorimetryHsystem = 0
Hsys = Hcal + Hrxn
Hrxn = -Hcal (all parts)
Hrxn = -mcTcal (all)
When Q reacts in a 1.5 kg calorimeter containing 2.5 kg water the temp changes from
22.50oC to 26.50oC.Calculate Hrxn. Cwater = 4.18 J/gK Ccal = 2.00 J/gK
In expensive calorimeters, the mass is constant; thus, the mc can be calculated together as C (J/oC).
Hrxn = -mcTcal
Hrxn = -CTcal
When X reacts in a 2.0 kg calorimeter containing 1.5 kg water, the temp changes
from 22.5oC to 30.5oC. Calculate Hrxn. Cwater = 4.18 J/gK Ccal = 1.50 J/gK
When X reacts in a 2.0 kg calorimeter containing 2.0 kg
water, T = 20.0oC to0.0oC. Calculate Hrxn.
50.0 % freezes.Hf = 334 J/g
Cwater = 4.18 J/gK Ccal = 2.00 J/gK
When 40.0 g NH4NO3 dissolves in 460.0 g water at 25.0oC, the temp. falls to 22.5oC. Calculate the Ho
per mole of NH4NO3.csoln = 4.00 J/gK
Topic:Thermochemical
Equation (TCE)
Thermo-chemical Equation
Terms
Heat of Reaction•The heat or enthalpy change of a chemical reaction
Hrxn
Typical Reaction
•HCl + NaOH NaCl + HOH
Heat of Solution
•The heat or enthalpy change when a substance is dissolved
Hsoln
Typical Ionization
KCl
K+(aq) + Cl-
(aq)
Heat of Combustion•The heat or enthalpy change when a substance is burned
Hcombustion
Combustion Reaction
•CxHy + O2
CO2 + HOH
Heat of Formation•The heat required to form one mole of a compound from pure elements
Hfo (kJ/mole)
Rxn Making Cpds from ele
H2 + ½ O2 H2O
The Degree Symbol•Indicates standard conditions & molar
quantities by itself or from a balanced
equation.
Gibb’s Free Energy•Energy of a system that can be converted to work
•Determines spontaneity
G
Exergonic Reaction•A reaction in which free energy is given off
G < 0
Endergonic Reaction
•A reaction in which free energy is absorbed
G > 0
Exergonic Reaction•A reaction which can be spontaneous
G < 0
Endergonic Reaction
•A reaction which cannot be spontaneous
G > 0
Reaction at Equilibrium
G = 0
Interrelation Term (G)
G interrelates thermochemistry,
chemical equilibria,
& electrochemistry
Energy of Formation•The energy required to form one mole of a compound from pure elements
Gfo (kJ/mole)
Entropy•A measure of disorder
S (J/K)
Entropy of Formation•The entropy of one mole of a substance
•Sfo (J/moleK)
•Sfo (kJ/moleK)
Thermochemical Equation
•An equation that shows changes in heat, energy, etc
Thermochemical Equation
Ho
rxn Hf
o
productsHf
o
reactants
Thermochemical Equation
Go
rxn Gf
o
productsGf
o
reactants
Thermochemical Equation
So
rxnSf
o
products
Sfo
r
eactants
Thermochemical Equation
•Stoichiometry of heat change
•Solves theoretical yield
Thermochemical Equation
•The 3rd step in stoichiometry involves converting what’s given to what’s asked for.
Thermochemical Equation
•Use the TCE for the 3rd step of stoichiometry to convert moles given to heat or free energy.
In stoichoimetric calculations, the TCE
is used for the conversion from mole
to heat, energy, or entropy.
Interrelating Equation
GH
S
Thermochemical Equation
Xo
rxn Xf
o
productsXf
o
reactants
Interrelating Equation
GH
S
Calc. H, G, & S when 13.6 g of CaSO4 is changed
into CaO + SO2 + O2 at 25oC
Cmpd CaSO4 SO2 CaO
Hf
o -1434.1 -296.8 -635.1
Gf
o -1321.8 -300.2 -604.0
Calculate H, G, & S when 19.7 kg of BaCO3 is decomposed into BaO + CO2
Cmpd BaCO3 CO2 . BaO
Hf
o -1216.3 -393.5 -553.5
Gf
o -1137.6 -394.4 -525.1
Sf
o
Drill: Calculate Ho
rxn &Go
rxn for:A + B2C3 AC2 + B
Compd B2C3 AC2
Hfo(kJ/mole) -150 -250
Gfo(kJ/mole) -175 -225
Calculate Ho, G
o, & S for
AD2 + BC AC2 + BD
at (-23oC)
Cpd BC AD2 AC2 BD
Hf
o -150 -250 -300 -175
Gf
o -125 -225 -250 -150
Sf
o 75 50 80 ?
Determine Sf
o
BD
Drill: Calculate Ho, Go, & So when P + QR PR2 + QCompd QR PR2
Hfo(kJ/mole) -250 -450
Gfo(kJ/mole) -225 -425
Ccup = 0.50 J/gK Cwater = 4.18 J/gK CNaOH = 1.00 J/gK
CThermometer = 2.00 J/gK
Required Constants
Lab Results: Cup H2O NaOH Thermo
5.0 g 50.0 g 2.0 g 20.0 g Ti = 22.0
oC Tf = 30.0
oC
Cmpd NaOH Na+ OH-
Hf
o -426.7 -240.1 -230.0
Determine: theoretical and experimental heat changes
Calculate the potential Ho, Go, & So for the reaction involving the burning of C3H8 Cpd C3H8 CO2 H2O
Hf
o-103.8 -393.5 -241.8
Gf
o- 23.5 -394.4 -228.6
Calculate the potential H, G, & S for the reaction & Sf
o for
O2 when burning 8.8 kg of C3H8 Cpd C3H8 CO2 H2O
Hf
o-103.8 -393.5 -241.8
Gf
o- 23.5 -394.4 -228.6
Sf
o269.9 213.6 188.7
Calculate Ho, Go, S, & at -23oC when: A + BC AC + B
Compd BC ACHf
o(kJ/mole) -150 -250Gf
o(kJ/mole) -175 -225
Drill: When 35.0 g NaOH dissolves in 965 mL water in a 2.5 kg calorimeter, the temp. went from 22.5oC to 26.5oC. Calculate: Ho
soln Csoln = 4.00 J/gK Ccal = 2.00 J/gK
TestReview
Calculate Ho, Go, & S at 227
oC for the production of
ammonia from N2 & H2.
Compd NH3
Hfo -46.1
Gfo -16.5
When 25.0 g CaCO3 is made
from CaO & CO2 in a 500. g calorimeter (C = 1.50 J/gK) containing 250.0 g of water
(C = 4.18 J/gK), the system changes from 25.0oC to 45.0oC. Calculate Hrxn/mole of CaCO3
Heat Change•Calculate the heat change when the temperature of 1.0 kg H2O is changed from –100.0oC to 200.0oC.
Bond Energy•The energy change
when one mole of bonds are broken
Ho
bond
Bond Equation
Hbondo
rxnHbond
o
products
Hbondo
reactant
s)
Bond Energies (kJ/mole)
C-C 347 O=O
C-H 414 498
O-H 464
C=O 715
Calculate the heat change when 1.00
mole of C2H6 is burned.
1st Law Thermodynamics
•Total energy change = heat + work
E = q + W
Work•W = Fd
•P = F/A
•V = Ad
•W = PV = nRT
2nd Law Thermodynamics
•Total entropy in a system always increases assuming no energy is added to the system
Thermodynamic Rxns are State
Rxns
State Reaction•Reactions that are independent of the
path; thus not dependent on intermediates
Drill: Calculate Ho, Go, & So when:
A + BC AC2 + BCompd BC AC2
Hfo(kJ/mole) -150 -268
Gfo(kJ/mole) -275 -220
Hess’s LawHrxn is the same
whether it occurs in a single step or a series
of steps.
Write TE for the process2 A + B C + D
C + A H
D + B 2 K
H + K M + B
K + M Product
Write TE for the process2 A + B C + D
C + A H
D + B 2 K
H + K M + B
K + M Product
2 A + B C + D
C + A H
D + B 2 K
H + K M + B
K + M Product
3 A + B Product
Write TE for the process2 A + 2 B C + D
C + A 2 H
D + B 2 K
H + K P + B
Write TE for the process2 A + 2 B C + D
C + A 2 H
D + B 2 K
2 H + 2 K 2 P + 2 B
Drill: Calculate Horxn for
the production of CaCO3 from CaO & CO2
Hf
o
(kJ/mole)
CaCO3 CaO CO2
-1206.9 -635.1 -393.5
Calculate the % yield from the
results of the last two slides
Bond Equation
Hbondo
rxnHbond
o
products
Hbondo
reactant
s)
Bond Energies (kJ/mole)
C-C 347 O=O
C-H 414 685
O-H 464
C=O 715
Calculate the heat change when 6.0
kg of ethane (C2H6) is burned
in excess oxygen.
Substance Hof(kJ/mole)
S Hof S Ho
f
A -100 H -150B -150 K -200C -50 P -250D -125 Q -300
Solve Horxn for TE
A + B 2 C + 2 D
C + A 2 H + P
D + B 2 K + P
H + K P + Q
Solve Horxn for TE
A + B 2 C + 2 D
2C + 2A 4 H + 2P
2D + 2B 4K + 2P
4H + 4K 4P + 4Q
Test on Thermochemistry
Tomorrow
Review
Calculate Htotal, when 40.0 g of
H2O is changed from - 25oC to
125oC. FPw = 0.0oC
BPw = 100.0 oC Hv = 2260 J/gCice = 2.06 (J/g K) Hf = 334 J/gCwater = 4.18 (J/g K)Csteam = 2.02 (J/g K)
Calculate Ho, Go, & So for N2O5 + H2O HNO3
Cpd N2O5 H2O HNO3 Hf
o -11.3 -285.8 -174.1
Gfo -10.4 -237.2 -151.5
When 10.8 g N2O5 is added to a
1.50 kg calorimeter (C = 1.00 J/gK) containing 1.00 kg of H2O
(C = 4.18 J/gK), the N2O5reacts with the water forming HNO3.
The temp. of the system changes from 23.000oC to 23.750oC.
Calculate the Hrxn/mole N2O5.
Calculate the % yield of the
reaction in the last two slides.
Solve Ho for TE X + Y 2 W + 2 Z 60 kJ
W + X 2 R + P 40 kJ
2 S + P Z + Y 50 kJ
R + S P + Q 80 kJ
Ho for TE X + Y 2 W + 2 Z 60 kJ
2W + 2X 4 R + 2P 80 kJ
2Z + 2Y 4 S + 2P -100 kJ
4 R + 4S 4P + 4Q 320 kJ
3X + 3Y 8P + 4Q 360 kJ
Calculate Ho, Go, & So for PbO2 + CO CO2 + Pb
Cpd PbO2 CO CO2 Hf
o -277.4 -110.5 -393.5
Gfo -217.4 -137.2 -394.4
Calculate: Teq & H of 48 g PbO2
Test Tomorrow
When 4.20 g MgCO3 is decomposed to MgO & CO2 in a 2500.0 g calorimeter (C = 2.00 J/gK) containing 1.0.kg of water (C = 4.18 J/gK), the water changes from 23.00oC to 13.00oC. Calculate the heat of rxn/mole of MgCO3