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Bettel Plus Chang Chemistry > Thermochemistry (Chang) > Flashcards

Thermochemistry (Chang) Flashcards

1
Q

Energy

A

Capacity to do work

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2
Q

Work

A

Directed energy change resulting from a process

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3
Q

Radiant energy/ solar energy

A

Comes from the sun; Earth’s primary energy source

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4
Q

Thermal energy

A

Energy associated with random motion of atoms and molecules

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5
Q

Kinetic energy

A

Energy produced by a moving object

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6
Q

Chemical energy

A

Stored within the structural units of chemical substances

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7
Q

Potential energy

A

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

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8
Q

Law of conservation of energy

A

Total quantity of energy in the universe is assumed constant

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9
Q

Heat

A

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

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10
Q

Thermochemistry

A

-study of heat change in chemical reactions

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11
Q

System

A

Specific part of the universe that is of interest to us

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12
Q

Surroundings

A

-the rest of the universe outside the system

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13
Q

Open system

A

Can exchange mass and energy with its surroundings

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14
Q

Closed system

A

Allows the transfer of energy (heat) but not mass

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15
Q

Isolated system

A

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

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16
Q

Exothermic process

A

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

energy products < energy reactants

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17
Q

Endothermic process

A

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

energy reactants < energy products

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18
Q

Enthalpy, H

A

H = E + PV

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19
Q

Enthalpy of reaction ∆H

A

∆H = Hprod - Hreact

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20
Q

Thermochemical equations

A

Show the enthalpy changes as well as the mass relationships

21
Q

Calorimetry

A

Measurement of heat changes

22
Q

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

A
  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

23
Q

Heat absorbed/ release

A

Q = ms∆T
Q = C∆T

24
Q

Constant volume bomb calorimeter

A

-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

25
Q

Constant-pressure calorimeter

A

-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)

26
Q

Standard enthalpy of formation, ∆H°f

A

-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

27
Q

Standard enthalpy of reaction, ∆H°rxn

A

Enthalpy of a reaction carried out at 1 atm

∆H°rxn = SUM(n. ∆H°f,products) - SUM(n. ∆H°f,reactants)

28
Q

Methods for determining ∆H°f
1. DIRECT METHOD

A

-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)

29
Q

Methods for determining ∆H°f
2. INDIRECT METHOD

A

-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

30
Q

Germain Henri Hess

A

Father of thermochemistry

31
Q

Heat of solution/
Enthalpy of solution, ∆Hsoln

A

-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)

32
Q

Dissolution of NaCl

A

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

33
Q

Lattice energy, U

A

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

34
Q

Heat of hydration, ∆Hhydration

A

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

35
Q

Heat of dilution

A

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

36
Q

Thermodynamics

A

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

37
Q

State of a system

A

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

38
Q

State functions

A

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

39
Q

First Law of Thermodynamics

A

-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

40
Q

Internal energy, E

A

•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

41
Q

Work

A

W = Fd
W = -P∆V

(if gas expanding on vacuum, P=0; W=0)

1 L.atm = 101.3 J

42
Q

Heat and work

A

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

43
Q

Enthalpy and the first law of thermodynamics

A

•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

44
Q

Walther Nernst

A

Third law of thermodynamics

45
Q

Fugacity of real gas is equal to

A

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

46
Q

Clausius Clapeyron does NOT apply to

A

S-L equilibrium

47
Q

What is Clapeyron Equation

A

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

48
Q

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?

A

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

Bettel Plus Chang Chemistry (19 decks)

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