Thermodynamics
Order of reaction
More kinetics...
General Equilibrium
Concentration and stoichiometry
100
When you touch an ice cube and it begins to melt in your hand, which of the following statements is true?
a) Heat flows from the ice cube into your hand.
b) The process is exothermic because the ice is melting.
c) Heat flows from your hand into the ice cube.
d) Entropy decreases as the ice melts.
C is true
100
Given the following information. What is the overall order of reaction?
A + B -> C + D
R = k [A]0[B]2
2nd order
100
True or false: A reaction proceeds faster when the activation energy is lowered.
True!
100
What is included in you equilibrium constant expression?
Gases and aqueous solutions
NOT LIQUIDS OR SOLIDS
100
If there is initially an equimolar amount of compound X and compound Y, identify the limiting reactant in the following reaction:
3X + 2Y → Z
X is the limiting reactant
200
Predict the signs for the following reaction that occurs when boiling water:
H2O(l)→H2O(g)
ΔH = +
ΔS = +
ΔG = - at high temperatures
200
What are the different ways in which you can determine the order of a reaction? Name at least three.
Rate law, experiments (tables), graph, rate constant units, given half life or integrated rate law
200
For the mechanism below, what is the function of the iodide ion, I- ?
Catalyst
200
Given the equilibrium, A(g) + B(g) → C(g), where will the equilibrium shift if we decrease the total volume?
To the right/towards products
200
How many mL of 1.2 M KOH solution are needed to prepare 25 mL of a 0.10 M solution?
2.1 mL
M1V1 = M2V2
V1 = (0.10M)(25mL)/(1.2)M
300
Predict the signs for the following reaction:
Ag+(aq)+Cl−(aq)→AgCl(s)
Hint: this is thermo, but think about solubility equilibrium as well!
ΔH = -
ΔS = -
ΔG = - at low temps
300
You are given the following rate constant:
k = 1.3 x 10^-5 1/s
What is the order of the reaction?
1st order
k units for a first order reaction = 1/s or s^-1
300
What is the reverse molecularity and reverse rate of the following elementary reaction?
H2 (g) + I2 (g) ⇋ 2HI (g)
Bimolecular
R = k^-1[HI]^2
300
In which case does Kc=Kp
2A(g)+B(s)⇄2C(s)+D(g)
2A(g)+B(s)⇄C(s)+2D(g)
3A(g)+B(s)⇄2C(s)+2D(g)
Number 2
total moles of gas = products - reactants = 0
300
What is the first thing you should do before solving concentration or stoichiometry problems?
Balance the equation (or just make sure it's balanced)!!
400
Consider the dissociation of hydrogen: H2(g)⇄2H+(g)
One would expect that this reaction:
Will be spontaneous at any temperature
Will be spontaneous at high temperatures
Will be spontaneous at low temperatures
Will not be spontaneous at any temperature
Number 2
breaking bonds = endothermic (+) and disordered (+)
G will be spontaneous (-) at high temperatures
400
What is the order of this reaction?
First order
400
How do you get a rate law from possible reaction mechanisms? Specifically, what part do you derive the rate law from?
The rate law is derived from the elementary step
NOT the overall reaction
400
Which of the following variables will help increase the production of O2?
6CO2 (g) + 6H2O (l) ⇋ C6H12O6 (s) + 6 O2 (aq) ΔH is positive
III and V
400
100 g of ethanol (C2H6) is dissolved in 100 g of water. The final solution has a volume of 0.2 L. What is the density of the resulting solution?
1000 g/L or 1g/mL
density = mass/volume
(100g ethanol + 100g water)/0.2L
500
Given the following thermochemical equations:
1. C(graphite)+1/2O2(g)→CO(g) ΔH=−110.5 kJ
2. CO(g)+1/2O2(g)→CO2(g) ΔH=−283.0 kJ
3. C(graphite)+O2(g)→CO2(g) ΔH=?
Determine what you have to do at each step to solve this problem, then solve.
Simply have to add the reactions for this problem
ΔH = -393.5
500
A reaction is thought to occur via the following elementary steps:
Step 1: 2A→B (slow)
Step 2: B+C→D (fast)
You are told that the graph of the reaction is linear at 1/[A] vs. time. Use both the reaction mechanisms and the graph to determine what the order is and whether the possible mechanisms is accurate.
2nd order (from both reaction mechanisms and graph)
The possible mechanisms are accurate because the order of the elementary step matches the order from the graph.
500
Given the mechanism:
Step 1: NO2+F2→NO2F+F (slow)
Step 2: F+NO2→NO2F (fast)
What is the rate-determining step? What is the rate law?
Rate-determining step = step 1
R = k[NO2][F2]
500
Consider the following reversible reaction at equilibrium:
PCl5(g)⇌PCl3(g)+Cl2(g)
The system is initially at equilibrium in a sealed container. Which of the following changes would decrease the concentration of Cl₂ at the new equilibrium?
a) Increasing the temperature
b) Adding more PCl₅
c) Removing some PCl₃
d) Decreasing volume
e) Adding an inert gas at constant volume
d.) Decreasing volume
More moles of gas on the product (right) side, decreasing volume will increase pressure and shift towards the side with fewer moles of gas, which is the reactant (left) side
500
A student mixes 50.0 mL of 0.100 M BaCl₂ with 50.0 mL of 0.100 M Na₂SO₄. A white precipitate of BaSO₄ forms according to the reaction:
Ba2+(aq)+SO42−(aq)→BaSO4(s)
After the reaction goes to completion, the student dilutes the resulting solution to 150.0 mL total volume.
Which of the following statements is true?
a) The final concentration of Na+ is 0.050 M.
b) The final concentration of Cl− is 0.033 M.
c) The limiting reactant is Na₂SO₄.
d) There is excess Ba²⁺ remaining in solution.
e) None of the above
e.) none of the above
no excess, no limiting reactant
[Na+], [Cl-] = 0.067 M (solve for moles of each, then dilute to 150 mL)