Chem Exam Review

Question 1

Define Exothermic

Answer 1

system transfers heat to surrounding. Temp increases, energy is released.

Question 2

Endothermic

Answer 2

system absorbs heat from surrounding. Temp decreases, energy is gained.

Question 3

How to calculate q[surroundings]?

Answer 3

q[surr]=mcΔT. +q = heat inc. -q = heat dec.

Question 4

What is Enthalpy? How do you calculate it?

Answer 4

Heat content. ΔH[sys]=-q[surr]. + ΔH endo, - ΔH exo

Question 5

How to calculate bond energy?

Answer 5

ΔH[rxn] = sum of reactant BE - sum of product BE

Question 6

How to calculate molar enthalpy?

Answer 6

ΔH[sys] = n ΔH[x] *used also as conversion factor

Question 7

How to calculate calorimetry with enthalpy?

Answer 7

n ΔH[x,sys] = -mc ΔT[surr]

Question 8

Methods for Communicating Thermochemical Equations?

Answer 8

Energy term, Enthaply value, Molar enthalpy, Potential Energy diagrams

Question 9

Energy terms and enthalpy value?

Answer 9

If e is reactant, rxn is endo. If e is product, rxn is exo. When enthalpy value is given (at end of equation) if + it is endo, if - it is exo.

Question 10

How to calculate Standard Enthalpy of Formation?

Answer 10

ΔH = sum of nΔH[f,products] - sum of nΔH[f,reactants]

Question 11

3rd Law of Thermodynamics

Answer 11

The S of perfectly ordered pure crystalline substance is 0 @ absolute zero. S = 0 @ T= 0K

Question 12

How to calculate entropy?

Answer 12

ΔS = sum of nS[products] - sum of nS[reactants]

Question 13

How to calculate Gibbs Free Energy?

Answer 13

ΔG = ΔH - T ΔS where S is in kj and T is in K.

ΔG = sum of n ΔG[f,products] - sum of n ΔG[f,reactants]

Question 14

What is the meaning of G?

Answer 14

ΔG<0, rxn is spontaneous in Fwd direction.
ΔG>0, rxn is nonspontaneous in Fwd direction.
ΔG=0, rxn is @ equilibrium

Question 15

How to calculate Reaction Rate?

Answer 15

Rate (r) = Δ[R/P] / Δt where R/P is reactant/product depending on whether consumption or production

Question 16

What is the Rate Law?

Answer 16

[A] -> Products : r = k[A]^m

[A] + [B] -> Products : r = k[A]^m[B]^n where m and n are the rate order, and m+n = overall rxn rate order

Question 17

What is the Transition State Theory?

Answer 17

Reactants transition to products with “enough energy”

Question 18

What is Activation Energy?

Answer 18

(E[a]) The sufficient amount of energy needed to break bonds and overcome repulsive forces.

Question 19

What is Collision Theory?

Answer 19

A successful collision is when there’s enough E[k] and the correct orientation.