Solutions
This solution is unstable and contains more dissolved solute than a saturated solution?
Supersaturated solution
What variable affects the colligative properties of a solution?
Concentration of solute particles
True or False?
Concentration changes the rate constant.
False, only temperature affects the rate constant.
N2 + O2 + heat ⇌ 2NO
a. decrease O2 concentration
b. add catalyst
a. decrease O2 concentration =Left
b. add catalyst = No Change
For a system at equilibrium, which of the following are true?
a) The rate of the reaction is zero.
b) The concentrations of reactants and products are no longer changing.
c) The value for the equilibrium constant, K, will change when temperature is changed.
d) The rate of the forward reaction is equal to the rate of the reverse reaction.
a) False: The rates forward and reverse are Equal
b) True
c) True -Only Temperature changes Keq
d) True
How does pressure affect solubility of a solid dissolving in liquid?
None
Which solution has a higher osmotic pressure?
2.0M KNO3
vs
3.5M Glucose
2.0M KNO3
This rate law has a rate constant, k, with units of M/s. What order is this reaction?
0 order
How will the following affect this reaction?
Shift Left, Right or No Change.
N2 + 3H2 ⇌ 2NH3 + heat
a. remove NH3 gas
b. decrease pressure
c. add N2 gas
d. increase temperature
a. remove NH3 gas =Right
b. decrease pressure = Left
c. add N2 gas = Right
d. increase temperature = Left
The equilibrium constant for the following reaction is equal to 0.447 at 100oC:
½ N2O4(g) <--> NO2(g)
a) What is the value for K for the following reaction:
2 NO2(g) <--> N2O4(g)
b) Write an expression for K, the equilibrium constant, for the reaction in (a).
a) Reaction = 2 x reverse of original reaction. So K2 = (1/K1)2 = (1/0.447)2 = 5.00.
b) K =[N2O4]/[NO2]2
Which molecule is more soluble in water?
MgS04 vs BaS04
BaS04
What is the molar mass of a nonelectrolyte if 80.0 g of the substance dissolved in 200.0 g of water has a freezing point of -4.65°C?
Kf = 1.86
160 g/mol
Define what is meant by unimolecular and bimolecular steps. Why are termolecular steps infrequently seen in chemical reactions?
The number of reactant molecules in a single molecular event.
Unimolecular means only one molecule is present as a reactant.
Bimolecular means two molecules are present as reactants
Termolecular means 3 molecules are present. This is rare, because it implies that all 3 molecules must collide simultaneously in order for the product/s to form. This usually happens in two steps with one molecular event leading to a reaction intermediate that collides with the 3rd molecule in a separate molecular event.
Consider the following system at equilibrium:
2 N2O(g) <--> 2 N2(g) + O2(g) H = +163 kJ
For each situation below, indicate whether more product or more reactant is produced in order to re-establish equilibrium.
a) the volume is increased
b) the temperature is increased
c) What effect will an increase in temperature have on the value for K?
a) more product made (the concentration is decreased so increase concentration)
b) more product made (endothermic reactions use up heat)
c) K will increase since increasing the temperature makes more product.
For the reaction below, K is 4.51 x 10-5 at 450oC.
N2(g) + 3 H2(g) <--> 2 NH3(g)
Is a mixture containing 100 atm NH3, 30 atm N2 and 500 atm H2 at equilibrium? If not, will the mixture shift toward product or reactants to achieve equilibrium?
Q = [NH3]2/[N2][H2]3
Q = (100)2/(30)(500)3 = 2.7 x 10-6
Q < K
Not at equilibrium. Reaction will shift toward product
Calculate the mole fraction of ethylene glycol (C2H602) when 120g of ethylene glycol are dissolved in 1.20 kg acetone (C3H6O).
0.0857
25.0g of solute is dissolved in 500mL of water. The osmotic pressure of the solution is 15.0mmHg at 25oC. What is the Molar Mass of the unknown molecule?
6.20x104 g/mol
k = .258 1/M*s at room temp
[A0] = .500M
a.) How long for the concentration to decrease by .383M?
b.) What is the half-life of this reaction?
a.) 1/[At] = kt + 1/[A0]
1/[0.500 - 0.383] = (0.258) t + 1/[0.500]
t = 25.4 s
b.) t1/2 = 1/k*[A0] = 7.75 s
For each reaction below, write an expression for K and indicate what effect an increase in pressure would have on equilibrium.
a) H2(g) + S(s) <--> H2S(g)
b) N2(g) + 3 H2(g) <--> 2 NH3(g)
c) H2(g) + Br2(l) <--> 2 HBr(g)
a) K = [H2S]/[H2] } No Effect
b) K = [NH3]2/[N2][H2]3 } Shift Right/ more product
c) K = [HBr]2/[H2] } Shift Left /more reactant
A mixture of 0.100 mol of NO, 0.050 mol of H2, and 0.100 mol of H2O are placed in a 1.00-liter flask. The following equilibrium is established:
2 NO(g) + 2 H2(g) <--> N2(g) + 2 H2O(g)
At equilibrium, [NO] = 0.070 M.
a) Calculate the equilibrium concentrations of H2, N2, and H2O.
b) Write an expression for K for this reaction.
c) Calculate K for this reaction.
d) At equilibrium, how will the concentrations of products compare to the concentrations of reactants?
a) [H2] = 0.020 M, [N2] = 0.015 M, [H2O] = 0.130 M
b.) K = [N2][H2O]2/[NO]2[H2]2
c.) K = [0.015][0.130]2/[0.070]2[0.020]2 = 130
d.) Since K is greater than 1, the concentration of products is greater than the concentration reactants; however since K is not extremely large, some reactants will remain at equilibrium.
You are given a solution of sucrose. How would you determine whether the solution was unsaturated, saturated or supersaturated?
Add a small crystal. If it dissolves, the solution was unsaturated. If it doesn't dissolve, the solution was saturated. If more than the crystal comes out of solution, then the solution was supersaturated.
A solution is 30.5%(m/m) of antifreeze (C2H6O2) in water. Calculate the freezing point depression and the freezing point temperature.
Kf = 1.86 °C kg mol¯1
1) Moles of antifreeze:
30.5%(m/m) means 30.5 g of C2H6O2 in 100 g of solution
30.5 g / 62.0674 = 0.4914 mol
2) Mass of water: 100 g − 30.5 g = 69.5 g = 0.0695 kg
3.) FP depression:
dTf = i*Kf*m = (1) (1.86 °C kg mol¯1) (0.4914 mol / 0.0695 kg)
dTf = 13 °C (leading to a freezing point of −13 °C)
NO (mol/L) Cl2 (mol/L) Rate (mol/L ⋅ min)
0.100 .100 .180
.100 .200 .360
.200 .201 .45
a.) What is the rate law?
b.) What is the value of the rate constant?
a.) rate = k[NO]2[Cl2]
b.) k = 1.8 x 102
Given the equilibrium constants for the following two reactions:
A(g) <--> B(g) K = K1
B(g) <--> C(g) K = K2
a) Derive the equilibrium constant for the reaction, A(g) <--> C(g) in terms of K1 and K2.
b) What general statement can be made about what happens to values for K when two reactions are added?
a.) K1 = [B]/[A]; K2 = [C]/[B];
K = [C]/[A] = K1 x K2
b) When a chemical equation is equal to the sum of two other chemical equations, then the equilibrium constant for the reaction is equal to the product of the equilibrium constants of the other two equations.
H2 (aq) + Br2 (aq) ⇌ 2HBr (aq)
Calculate all three equilibrium concentrations when 0.500 mole each of H2 and Br2 are mixed in a 2.00 L container and Kc = 36.0.
36.0 = (2x)2 / (0.250 - x)(0.250 - x)
x = 0.1875
[H2] = 0.0625 M
[Br2] = 0.0625 M
[HBr] = 0.375 M