Thermochemistry

Question 1

the energy of a system can be changed either by heat transfer, or by doing work
only two ways in which energy can enter/leave a system

Answer 1

conservation of energy of a system

Question 2

first law of thermodynamics

energy can never be created or destroyed

Answer 2

conservation of energy

Question 3

Equation: Energy of a system: ∆E

Answer 3

∆E = q - W
SI Unit= Joule?
Note: q = heat absorbed by the system from its surroundings; W is the work done BY the system on its surroundings
***If W is work done ON the system by the surroundings, then ∆E = q + W

Question 4

energy transfer that occurs as a result of a temperature difference between the system and its surroundings
transfer will occur spontaneously from a warmer system to a cooler system
measured in the same units as Energy (Joules), calories (cal), kcal (kilocalorie), or kJ (kilojoule)

Answer 4

Heat

Question 5

process in which heat is transferred from one particle to another through collisions
metals are good ______ of heat

Answer 5

conduction

conductors

Question 6

transfer of energy by electromagnet waves
type of heat transfer does not require a material medium
can occur in a vacuum
how the sun warms the earth

Answer 6

radiation

Question 7

transfer of heat by the bulk movement of fluids

Ex: warm air rises and cool air falls b/c of the difference in density

Answer 7

convection

Question 8

functions whose value depends only on the position of the system and not on how the system got there
Ex: elevation is an example but distance traveled it not

Answer 8

state function

Question 9

measure of the disorder, or randomness, of a system

units = Energy / temperature = J/K or cal/K (often J*K/mol)

Answer 9

entropy (S)

Question 10

states that all spontaneous processes proceeding in an isolated system lead to an increase in entropy

Answer 10

second law of thermodynamics

Question 11

states that the absolute entropy of a pure crystalline substance at absolute zero is zero
corresponds to a state of “perfect order” bc all of the atoms in the hypothetical state possess no kinetic energy and do not vibrate at all, so there is absolutely no randomness and no disorder in the spatial arrangement of the atoms

Answer 11

third law of thermodynamics

Question 12

phases of matter w/ increasing entropy

Answer 12

solid < liquid < gas

Question 13

Dissolution of particles in solution ________ the entropy

Answer 13

increases

Question 14

Entropy _______ with temperature

Answer 14

increases

Question 15

measure of the “heat content” of a system

Answer 15

Enthalpy (H)

Question 16

equal to the heat absorbed or evolved by the system at constant pressure

Answer 16

∆H; change in enthalpy

Question 17

change in enthalpy that corresponds to an endothermic process (one that absorbs heat)
*products at higher PE than reactants

Answer 17

+∆H

Question 18

change in enthalpy that corresponds to an exothermic process (releases heat)
*products at lower PE than reactants

Answer 18

-∆H

Question 19

the enthalpy change that would occur if one mole of that compound were formed directly from its elements in their standard states
Ex: formation of water = enthalpy change of the rxn between 1 mole of diatomic hydrogen and 1/2 mole of diatomic oxygen

Answer 19

standard enthalpy (or heat) of formation of a compound (∆Hºf)

Question 20

∆Hºf of an element in its standards state

Answer 20

= zero

Question 21

hypothetical enthalpy change that would occur if he reaction were carried out under standard conditions
i.e. when reactants in their standard states are converted to products under standard conditions (1 atm and usually 298 K)

Answer 21

standard heat of reaction (∆Hºrxn)

Question 22

Equation: Standard heat of rxn (∆Hºrxn)

Answer 22

∆Hºrxn = (sum of ∆Hºf of products) - (sum of ∆Hºf of reactants)
*Note: multiply ∆Hºf by the stoichiometric coefficient; switch sign if compound is broken down instead of formed

Question 23

states that if a reaction can be broken down into a series of steps, the enthalpy change for the overall net reaction is just the sum of the enthalpies of each step
consequence of enthalpy being a state function

Answer 23

Hess’s Law

Question 24

describes the overall spontaneity of a reaction

Answer 24

Gibbs Free Energy (∆G)

Question 25

Equation: Gibbs Free Energy

Answer 25

∆G = ∆H - T∆S

Question 26

indicates a spontaneous reaction

Answer 26

• ∆G

Question 27

indicates a nonspontaneous reaction

Answer 27

+ ∆G

Question 28

indicates that system is not in a state of equilibrium

Answer 28

∆G = 0

Question 29

-∆H and +∆S: rxn is _______ at all temperatures

Answer 29

spontaneous (-∆G)

Question 30

+∆H and -∆S: rxn is _______ at all temperatures

Answer 30

not spontaneous (+∆G)

Question 31

+∆H and +∆S: rxn is _______ only at high temperatures

Answer 31

spontaneous (-∆G)

Question 32

-∆H and -∆S: rxn is _______ only at low temperatures

Answer 32

spontaneous (-∆G)

Question 33

the amound of heat needed to raise the temperature of one mass unit of a substance by 1 degree Celsius

Answer 33

Specific Heat (c)

Question 34

Equation: Amount of heat (q) gained or given off by a substance that changes in temp

Answer 34

q = mc∆T

Question 35

amount of heat required to change the phase of one mass unit of a substance

Answer 35

heat of transformation (L)

Question 36

Equation: amount of heat (q) gained or given off by a substance that cahnges phase

Answer 36

q = m * L

Question 37

During a phase change, the _______ of a system stays constant

Answer 37

temperature

Question 38

The thermal energy supplied to a system during a phase change is used to increase the ______ of the substance instead of the KE, which corresponds to temperature

Answer 38

Potential Energy (PE)

Question 39

Breaking bonds ______ energy.

Answer 39

Requires

Question 40

Melting, vaporization, and sublimation are all ________ phase changes

Answer 40

endothermic (require energy)

Question 41

Forming bonds ________ energy

Answer 41

releases

Question 42

Freezing, condensation, and deposition are all ________ phase changes

Answer 42

exothermic

Question 43

corresponds to the energy needed to effect the phase change from ice to water (solid to liquid)

Answer 43

heat of fusion: ∆H(fusion)

Question 44

corresponds to the energy needed to effect the phase change from water to vapor

Answer 44

heat of vaporization: ∆H(vap)

Question 45

phase change from solid to liquid

Answer 45

fusion

melting

Question 46

phase change from liquid to solid

Answer 46

freezing

Question 47

phase change from liquid to gas

Answer 47

vaporization

Question 48

phase change from gas to liquid

Answer 48

condensation

Question 49

phase change from solid to gas

Answer 49

sublimation

Question 50

phase change from gas to solid

Answer 50

deposition

Question 51

point (on phase diagram) at which all three phases are in equilibrium (solid, liquid, and gas) at a certain temp and pressure unique to that substance

Answer 51

triple point

Question 52

point (on a phase diagram) at which the differences between the properties of the liquid and gas phases disappear
at extremely high temperature and pressure
beyond this point, the substance exists as a supercritical fluid

Answer 52

critical point