Thermochemistry

Question 1

Isolated system

Answer 1

Cannot exchange energy or matter with surroundings

Question 2

Closed system

Answer 2

cahn exchange energy but not matter

Question 3

Open system

Answer 3

can exchange heat and energy i.e. pot of boiling water

Question 4

Delta U = Q + W

Answer 4

delta U: change in internal energy of the system

Q: heat added to the system

W: work done by the system

Question 5

Isothermal processes

Answer 5

System’s temperature is constant. Q = W

Question 6

Adiabatic processes

Answer 6

No heat exchanged between system and environment. (delta) U = -W

Question 7

Isobaric processes

Answer 7

Pressure of system is constant.

Question 8

Isovolumetric processes (isochoric)

Answer 8

No change in volume. No work is performed in process. (delta U) = Q

Question 9

Spontaneous process

Answer 9

A process that can occur by itself or without having to be driven by energy from an outside source. (delta) G helps us predict spontaneity

Question 10

Standard Conditions

Answer 10

25°C (298K), 1 atm, 1M concentrations; used for measuring enthalpy, entropy, and Gibbs free energy

Question 11

Standard Temperature and Pressure

Answer 11

0°C (273K), 1 atm

Question 12

Gas-liquid equilibria

Answer 12

molecules near surface of liquid may have enough energy to jump into gas phase.

Question 13

Condensation

Answer 13

Gas to liquid. Facilitated by lower temperatures or higher pressures

Question 14

Sublimation

Answer 14

Solid to gas.

Question 15

Deposition

Answer 15

Gas to solid

Question 16

Enthalpy

Answer 16

Average KE of particles and amount of substance present.

(H)

(delta) H_rxn = H_products - H_reactants

+ enthalpy = endothermic

• enthalpy = exothermic

Question 17

Heat

Answer 17

Transfer of energy from one substance to another as a result of a difference in temperature. (Q)

Q > 0: endothermic

Q < 0: exothermic

Question 18

Zeroth Law of Thermochemistry

Answer 18

Objects are only in thermal equilibrium when their temperaturs are equal.

Question 19

q= mc(delta)T

Answer 19

q: heat absorbed or release (J or cal)
m: mass
c: specific heat (cal/g x K)

c_H20 = 1 cal/g x K

Question 20

heat capacity

Answer 20

mass x specific heat

Question 21

Heating Curve

Answer 21

Question 22

q = mL

Answer 22

m = mass

L= Latent heat (cal/g)

Used during phase changes

Question 23

Standard enthalpy of formation

(delta)H_f°

Answer 23

The enthalpy required to produce one mole of a compound from its elements in their most stable physical states (standard states).

Question 24

Standard heat of a reaction

(delta)H°_rxn

Answer 24

ΣH°_f,products - ΣH°_f,reactants

Question 25

Hess’s Law

Answer 25

(delta)H = (delta)H₁ + (delta)H₂+(delta)H₃ + (delta)H₄

Question 26

Bond dissociation energy

Answer 26

Energy needed to break a type of bond between atoms in the gas phase. (endothermic)

KJ/mol of bonds broken

Question 27

Standard heat of combustion

(delta)H°_comb

Answer 27

The enthalpy change associated with the combustion of a fuel.

Question 28

Second Law of Thermodynamics

Answer 28

Energy spontaneously disperses from being localized to becoming spread out if it is not hindered from doing so.

Question 29

Entropy

Answer 29

The measure of spontaneous dispersal of energy at a specific temperature. How much energy is spread out, or how widely spread out energy becomes, in a process.

(Delta)S = Q_rev/T

Q_rev = heat that is gained or lost in a reversible process

T = temp in Kelvin

Units: J/(mol x K)

Question 30

Gibbs free energy

Answer 30

Measure of change in enthalpy and entropy; predicts whether a process is spontaneous or nonspontaneous.