Thermochemistry (Chang)

Question 1

Energy

Answer 1

Capacity to do work

Question 2

Work

Answer 2

Directed energy change resulting from a process

Question 3

Radiant energy/ solar energy

Answer 3

Comes from the sun; Earth’s primary energy source

Question 4

Thermal energy

Answer 4

Energy associated with random motion of atoms and molecules

Question 5

Kinetic energy

Answer 5

Energy produced by a moving object

Question 6

Chemical energy

Answer 6

Stored within the structural units of chemical substances

Question 7

Potential energy

Answer 7

Energy available by virtue of an object’s position

*Chemical energy can be considered as form of potential energy because it is associated with relative positions and arrangements of atoms within a given substance

Question 8

Law of conservation of energy

Answer 8

Total quantity of energy in the universe is assumed constant

Question 9

Heat

Answer 9

Transfer of thermal energy between two bodies that are at different temperatures (hot to cold)

Question 10

Thermochemistry

Answer 10

-study of heat change in chemical reactions

Question 11

System

Answer 11

Specific part of the universe that is of interest to us

Question 12

Surroundings

Answer 12

-the rest of the universe outside the system

Question 13

Open system

Answer 13

Can exchange mass and energy with its surroundings

Question 14

Closed system

Answer 14

Allows the transfer of energy (heat) but not mass

Question 15

Isolated system

Answer 15

-totally insulated container
-does not allow the transfer of either mass or energy

Question 16

Exothermic process

Answer 16

-any process that gives off heat; transfers thermal energy to surroundings

energy products < energy reactants

Question 17

Endothermic process

Answer 17

-heat has to be supplied to the system by the surroundings

energy reactants < energy products

Question 18

Enthalpy, H

Answer 18

H = E + PV

Question 19

Enthalpy of reaction ∆H

Answer 19

∆H = Hprod - Hreact

Question 20

Thermochemical equations

Answer 20

Show the enthalpy changes as well as the mass relationships

Question 21

Calorimetry

Answer 21

Measurement of heat changes

Question 22

(1) Specific heat, s
and
(2) Heat capacity, C

Answer 22

1. Amount of heat required to raise the temperature of one gram of substance by one degree C
2. Amount of heat required to raise the temperature of a given quantity of the substance by one degree C

C = ms

Question 23

Heat absorbed/ release

Answer 23

Q = ms∆T
Q = C∆T

Question 24

Constant volume bomb calorimeter

Answer 24

-constant volume of container
-Combustion reaction: heat of combustion
-“bomb”: refers to explosive nature of the reaction in the presence of oxygen gas

Qsys = Qwater + Qbomb + Qrxn = 0
Qwater = ms∆T
Qbomb = Cbomb.∆T

Question 25

Constant-pressure calorimeter

Answer 25

-heat changes for non-combustion reactions -acid base neutralizations; heat of solution and heat of dilution Qrxn = ∆H Qsys = Qsoln + Qcal + Qrxn = 0 (assuming no heat loss to surroundings)

Question 26

Standard enthalpy of formation, ∆H°f

Answer 26

-Heat change that results when one mole of a compound is formed from its elements at a pressure of 1 atm -standard enthalpy of formation of any element in its most stable form is zero -elements: standard state at 1 atm

Question 27

Standard enthalpy of reaction, ∆H°rxn

Answer 27

Enthalpy of a reaction carried out at 1 atm ∆H°rxn = SUM(n. ∆H°f,products) - SUM(n. ∆H°f,reactants)

Question 28

Methods for determining ∆H°f 1. DIRECT METHOD

Answer 28

-for compounds that can be readily synthesized from their elements i.e. C(graphite) + O2(g) ➡️ CO2(g) 1. Measure ∆H°rxn 2. Use ∆H°rxn = SUM(n. ∆H°f,products) - SUM(n. ∆H°f,reactants)

Question 29

Methods for determining ∆H°f 2. INDIRECT METHOD

Answer 29

-used for compounds that cannot be directly synthesized from their elements -Use HESS'S LAW: when reactants are converted to products, the change in enthalpy is the same whether the reaction takes place in one step of into a series of step

Question 30

Germain Henri Hess

Answer 30

Father of thermochemistry

Question 31

Heat of solution/ Enthalpy of solution, ∆Hsoln

Answer 31

-Heat generated or absorbed when a certain amount of solute dissolves in a certain amount of solvent -may either be - (exothermic) or + (endothermic) depending on the nature of cation/ anion ∆Hsoln = Hsoln - Hcomponents (∆Hsoln: measured using constant pressure calorimeter)

Question 32

Dissolution of NaCl

Answer 32

NaCl in solid state ➡️ (1) Latice energy (+): Na+ Cl- ions in gaseous state ➡️ (2) Heat of hydration (-): water molecules shield Na+ and Cl- from each other Heat of soln: ∆Hsoln = U + ∆Hhydra

Question 33

Lattice energy, U

Answer 33

Energy required to completely separate one mole of solid ionic compound into gaseous ions

Question 34

Heat of hydration, ∆Hhydration

Answer 34

-enthalpy change associated with hydration process -negative quantity for cations and anions

Question 35

Heat of dilution

Answer 35

-heat change associated with the dilution process -(endothermic) more heat absorbed when diluted -(exothermic) more heat released when diluted

Question 36

Thermodynamics

Answer 36

-study of the interconversion of heat and other kinds of energy

Question 37

State of a system

Answer 37

-the values of all relevant macroscopic properties (i.e. composition, energy, temperature, pressure volume)

Question 38

State functions

Answer 38

-properties that are determined by the state of the system, regardless of how that condition was achieved (energy, temperature, pressure and volume)

Question 39

First Law of Thermodynamics

Answer 39

-based on law of conservation of energy -energy can be converted from one form to another but cannot be created nor destroyed ∆Esys = -∆Esurr ∆Esys = Q + W (+) Q: endothermic (-) Q: exothermic (+) W: done on the system (-) W: done by the system

Question 40

Internal energy, E

Answer 40

•Kinetic energy: various types of molecular motion and the movement of electrons within molecules •Potential energy: attractive attractions between electrons and nuclei and by repulsive interactions between electrons and between nuclei in individual molecules, as well as interactions between molecules

Question 41

Work

Answer 41

W = Fd W = -P∆V (if gas expanding on vacuum, P=0; W=0) 1 L.atm = 101.3 J

Question 42

Heat and work

Answer 42

-path functions -not properties of a system; manifest only during a process/ change

Question 43

Enthalpy and the first law of thermodynamics

Answer 43

•Constant-volume ∆E = Q •Constant-pressure ∆E = Q - P∆V ∆H = ∆E + P∆V Q = ∆H *kapag may gas sa product, ipupush ung piston pataas (expansion) (Another way for ∆E of gaseous rxn: assume ideal gas behavior and constant temperature) ∆E = ∆H - RT∆n ∆n = moles product gases - moles reactant gases

Question 44

Walther Nernst

Answer 44

Third law of thermodynamics

Question 45

Fugacity of real gas is equal to

Answer 45

The pressure of an ideal gas which has the same chemical potential as the real gas

Question 46

Clausius Clapeyron does NOT apply to

Answer 46

S-L equilibrium

Question 47

What is Clapeyron Equation

Answer 47

It postulates that if the temperature and pressure are both change in such a way as to keep the chemical potentials of two phases equal to each other, the rates of change are given by the equation

Question 48

The coexistence curve where the plot of pressure vs temperature along which the two phases coexist was shown by Clausius-Clapeyron. What did Clausius postulate?

Answer 48

The clapeyron equation was simplified by assuming that the vapor oneys the ideal gas law and by neglecting the molar volume of the gas in comparison with molar volume of the liquid