Unit I: Thermodynamics, Kinetics

Question 1

1st Law of Thermodynamics

Answer 1

energy can be converted from one form to another but cannot be created or destroyed

Question 2

Enthalpy

Answer 2

• known as H, units are KJ/mole
• energy in a system plus work on the system or internal energy plus product of pressure and volume

Question 3

specific heat capacity

Answer 3

• denoted by “c”
• quantity of heat required to change 1 gram of a substance by 1 K (J/g*K)

Question 4

Equation when given any of following: specific heat capacity, mass, change in temperature, heat.

Answer 4

q = m x c x ΔT

q is heat in joules

m is mass

c is specific heat capacity

T is temperature

Question 5

Hess’s Law

Answer 5

the enthalpy change of an overall process is the sum of the enthalpy changes of its individual steps

Question 7

Bond Energy

Answer 7

energy needed to overcome the attraction between two atoms

Question 8

Bond Order

Answer 8

• # of electron pairs shared by two atoms
• single bond = 1, etc.

Question 9

Bond Length

Answer 9

distance between nuclei of two bonded atoms

Question 10

Heat of Vaporization

Answer 10

Δ Hvap - heat required to vaporize something (KJ/mole)

Question 11

Heat of Fusion

Answer 11

Δ Hfus - heat required to melt something (KJ/mol)

Question 12

entropy

Answer 12

• randomness, the freedom of motion of particles in a system
• greater freedom = greater # particles = more systemic disorder = greater entropy

Question 13

2nd Law of Thermodynamics

Answer 13

• entropy of the universe increases _for spontaneous processes _

Question 14

3rd Law of Thermodynamics

Answer 14

• entropy of a perfect crystalline solid is zero at absolute zero ( 0 K)
• this basically means there is entropy in everything since perfection and absolute zero are non-existent in nature

Question 15

Gibbs Free Energy Equation

Answer 15

ΔG = ΔH - TΔS

• G is free energy, H is enthalpy, S is entropy, T is temperature
• if ΔG < 0, rxn is spontaneous
• ΔG > 0, rxn is not spontaneous
• ΔG = 0, rxn is in equilibrium

Question 16

Rate Law

Answer 16

• predicts how fast a reaction will occur given the initial concentration of reactants
• rate = K[A]^x[B]^y
• k is the rate constant
• A and B are reactants, [] means concentration
• X and Y are the ‘orders’ of each reactant, determined experimentally

Question 17

1st Order Integrated Rate Law

Answer 17

ln [A]₀/[A]_t = Kt

Question 18

2nd Order Integrated Rate Law

Answer 18

1/[A]_t - 1/[A]_{0 =} Kt

Question 19

Zeroth Order Integrated Rate Law

Answer 19

[A]_t - [A]₀ = -Kt

Question 20

Half Life

Answer 20

• the amount of time for concentration of a reactant to decrease to half its initial concentration

Question 21

1st Order Half Life Equation

Answer 21

(ln 2)/k = t_1/2

Question 22

Activation Energy

Answer 22

• the energy threshold that must be reached for a reaction to occur (KJ/mol)
• the “hill” on a reaction pathway graph

Question 23

Transition State

Answer 23

• the species formed by reactant molecules before products are generated, defined by its insignificant lifetime

Question 24

Arrhenius Equation for 2 rate constants and 2 temperatures

Answer 24

ln (K₂/K₁) = - E_a/R(1/T₂-1/T₁)

Question 25

Intermediate

Answer 25

• a compound that appears in a chemical mechanism but is not seen in the overall reaction
• it is generated and then consumed
• unlike transition state, it has a lifetime

Question 26

Catalyst

Answer 26

• a substance that lowers the activation barrier of a reaction, but is not consumed by the reaction