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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.

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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

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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)

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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)

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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

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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

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Thermodynamic Terms

Heat, q. Work, w. Internal energy, E or U System Surroundings Enthalpy, H State Functions

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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.

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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

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Internal Energy

E or U The total kinetic and potential energy of a

molecule or ion• Molecular motion• Electronic changes

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Molecules Store Energy inMolecular Motion

translation

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Electronic Changes

endothermicchange in electron

energy levelsO h Otriplet oxygen singlet oxygen

OH H OH H

exothermicbond formation

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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?

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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

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Internal Energy

translation

The total energy (E or U) of a molecule or ionis due to all sources of kinetic and potential energy.

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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?

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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