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Chemical Reactions Problem Set.
ThermochemistryFirst Law of Thermodynamics
Edward A. Mottel
Department of Chemistry
Rose-Hulman Institute of Technology
04/19/23
Chemical Thermodynamics
Reading assignment: • Chang: Chapter 6.1-6.3
A study of the energy changes which accompany the physical and chemical changes of matter.
04/19/23
A Thermodynamic Term
Enthalpy
The total heat energy contentof a molecule.
If a chemical processrequires heat,the enthalpy changeis endothermic.
If a chemical processreleases heat,
the reaction changeis exothermic.
04/19/23
Solution ReactionsEndothermic and Exothermic
NH4+(aq) + NO3
–(aq)
Hsoln = +25.8 kJmol–1
2 H+(aq) + SO42–(aq)
Hsoln = -96.2 kJmol–1
exothermic
NH4NO3(s)H2O
H2SO4(conc)H2O
enthalpy of solution endothermic
04/19/23
Changes in Physical StateReactions should be balanced and
annotated
Enthalpy of vaporization of water
Enthalpy of sublimation of water
Enthalpy of fusion of water
H2O(g) H2O(l)
H2O(g) H2O(s)
H2O(l) H2O(s)
04/19/23
Chemical ReactionsExamples
Decomposition
Single replacement
Double replacement
Cr2O3(s) + N2(g) + 4 H2O(g) (NH4)2Cr2O7(s)
2 NaCl(aq) + I2(aq)2 NaI(aq) + Cl2(g)
NaCl(aq) + H2CO3(aq) HCl(aq) + NaHCO3(s)
04/19/23
Chemical ReactionsCombustion and Formation
Combustion
Formation
2 CO2(g) + 3 H2O(g) C2H5OH(l)+ 3 O2(g)
Na2CO3(s)2 Na(s) + C(gr) + 3/2 O2(g)
carbon is converted to
hydrogen is converted to
most common elemental form
04/19/23
Combustion of sucrose (C12H22O11)
Formation of sucrose
12 CO2(g) + 11 H2O(g) C12H22O11(s) + 12 O2(g)
C12H22O11(s)12 C(gr) + 11 H2(g) + 11/2 O2(g)
Write the equationfor each of the following processes
more examples
04/19/23
Thermodynamic Terms
Heat, q. Work, w. Internal energy, E or U System Surroundings Enthalpy, H State Functions
04/19/23
Thermal Energy
q
What is the difference betweenheat and temperature?
Are heat and temperatureintensive or extensive properties?
Heat flows form a warmer body to a cooler body.
04/19/23
Work
FFFFFFFFFFFFFFFFFFFFFFFFw = F·d
d
Work has an intensive and a capacitive factor.
What is the difference betweenwork and being tired?
Work
Type of Work
mechanical
expansion
electrical
Intensity
force
pressure
potentialdifference
Capacity
distance
volume change (dV)
amount of electricity(charge)
gravitational gravity height x mass
04/19/23
Internal Energy
E or U The total kinetic and potential energy of a
molecule or ion• Molecular motion• Electronic changes
04/19/23
Molecules Store Energy inMolecular Motion
translation
04/19/23
Electronic Changes
endothermicchange in electron
energy levelsO h Otriplet oxygen singlet oxygen
OH H OH H
exothermicbond formation
04/19/23
First Law of Thermodynamics
U = energygained - energylost
The change in internal energy of a system isequal to the energy added to the system,
minus the energy lost by the system.
25 ºC200 ºC400 ºC800 ºC
E = q + w
First Law of Thermodynamics
The change in internal energyis equal to the heat added and the work done on the system.
What’s happeningto the gas
in the rigid bulb?
04/19/23
Closed system Isolated system
q
Surroundings - Everything else(the rest of the universe).
System - any region of space or materialwhich is considered in dealing with
energy changes that matter undergoes.
mm
04/19/23
Internal Energy
translation
The total energy (E or U) of a molecule or ionis due to all sources of kinetic and potential energy.
04/19/23
1.0 atm1.1 atm 1.2 atm 1.3 atm 1.4 atm 1.5 atm 1.6 atm 1.7 atm 1.8 atm 2.0 atm 2.3 atm 2.7 atm 3.2 atm
First Law of Thermodynamics
E = q + w
4.0 atm
What’s happening to the temperature of the gas?Why?
04/19/23
First Law of Thermodynamics
E = q + w
Explain what is happeningusing the First Law of Thermodynamics.
1.0 atm1.0 atm1.0 atm1.0 atm1.0 atm1.0 atm1.0 atm1.0 atm1.0 atm1.0 atm1.0 atm1.0 atm1.0 atm1.0 atm1.0 atm