SA 3 Flashcards
0.770 mol hydrogen iodide (HI) is introduced into a 2.0 L vessel and allowed to reach equilibrium at 700 K as represented by the following reaction.
2HI(g) ⇌ H2(g) + I2(g)
What is the concentration of I2 at equilibrium if the concentration of HI at equilibrium is 0.300 M?
- ICE table
- I2 = x, no overthinking
I2 = 0.0425
3.0 mol of SO2 and 2.0 mol of O2 are made to come to equilibrium in a 5.0 L container according to the equation:
2SO2(g) + O2(g) ⇌ 2SO3(g)
At equilibrium the concentration of SO2 is found to be 0.40 M. At this temperature, what is the value of the equilibrium constant?
- ICE
- Kc (don’t forget coefficients)
0.83
2NOCl(g) ⇌ 2NO(g) + Cl2(g) Kc = 1.6 × 10–5 at 35 °C.
What is the value of the equilibrium constant, at 35 °C, for the following equilibrium?
NO(g) + ½Cl2(g) ⇌ NOCl(g)
- if Kc is not there, find it
- reverse reaction = 1/old Kc (if Kc is 15, new Kc is 1/15)
- it’s not multiply or divide, its square or 1/square thing (if x2 = 15^2, if /2 = 15^1/2)
2.5 x 10^2
What does ‘hydrolize’ mean?
break down of chemical reaction due to water
For the following the following equilibrium:
2H2O(g) + 2Cl2(g) ⇌ 4HCl(g) + O2(g) Kc = 5.0 x 10–4 at 375 K
Which one of the following will be correct?
a. 2[O2] > [Cl2]
b. [O2] = 4[HCl]
c. 2[Cl2] > [HCl]
d. 2[HCl] = [Cl2]
b. 2[Cl2] > [HCl]
The Kc for a reaction was found to be 1.2 at a certain temperature. The equilibrium was disturbed and the value of Qc was found to be 6.25 at the same temperature.
Where will the equilibrium shift to reestablish equilibrium?
Qc > Kc so products are favored, equilibrium shifts to the left
Consider the following equilibrium:
CO(g) + 2H2(g) ⇌ CH3OH(g) ∆H = −18 kJ mol–1
Use Le Châtelier’s principle, to state how decreasing the volume of the system will affect the number of moles of CH3OH present at equilibrium.
- rmb that volume correlates to concentration
The moles of CH3OH will increase because the equilibrium shifts to the right.
N2O4(g) ⇌ 2NO2(g) ∆H is positive
If the temperature increased, where will the equilibrium shift?
- decrease in temp = endo
- increase in temp = exo
- system wants to reverse the change (exo become endo, endo become exo)
equilibrium shifts to the right
Which statement(s) is/are correct regarding the reaction below?
N2(g) + 3H2(g) ⇌ 2NH3(g) ∆H= –92 kJ mol–1
I An increase in pressure will shift the equilibrium to the right.
II An increase in temperature will shift the equilibrium to the right.
III A catalyst will shift the equilibrium to the right.
I only
The pH of a 0.090 M solution of the weak acid nitrous acid was measured to be 2.20. What is the [H+]?
- pH = -log(H+)
- log_a n = x –> a^x = n
- [H+] = 10^pH
6.3 x 10^-3
100 mL of 0.10 M NaOH and 100 mL of 0.20 M HCl are mixed. What is the pH of the resulting solution?
-1. calculate mole
When the pH of a solution changes from 9 to 12, what happens to the hydrogen ion concentration?
The hydrogen ion concentration decreases by a factor of 1000
What is the pH of H3O+ when the concentration is 4.2 x 10^-3
- -log(OH-)
- 14 - pOH
11.6
If the Ka of an acid is 1.8 x 10^-5, calculate the pKa and pKb value
- -log(Ka)
pKa = 4.74 - pKa + pKb = 14
pKb = 9.26
If H3O+ = 7.1 x 10^-2, what is the concentration of [OH-]
- find pOH
- find pH
- OH- = 10^-pH
1.4 x 10^-13 M
If the pKa of an acid is 3.7, what is the Kb value?
- pKa + pKb = 14
- Kb = 10^-pH
5.01 x 10^-11
For the reaction represented by the equation H2(g) + F2(g) ⇌ 2HF(g), the equilibrium constant at 25 °C is 313.
At the same temperature, what is the value of K for the following? HF(g) ⇌ ½H2(g) + ½F2(g)
5.65 x 10^–2
3.2 g of a gaseous compound occupies 2.6 L at 273 K and 1.00 atm.
What is the molar mass of this compound?
28 g mol–1
What is the molar volume of nitrogen gas at 185 kPa and 125 °C?
- use pV = nRT
- molar volume = M/V (use V/n = RT/p)
17.9 L mol–1
Do the bonds that turn solid to liquid require or release energy?
Require (bonds are broken)
Do the bonds that turn liquid to solid require or release energy
Release (bonds become tighter)
How much energy is released when 1.25g of NaF changes from liquid to solid at melting point, ∆Hfus = 29.3 kJ mol^-1
- convert to mol
- multiply mol with ∆Hfus (m/Mr x ∆Hfus)
0.872 kJ mol^-1
What is the gas constant when the pressure is
i. in atm
ii. in kPa
i. 0.0821 L atm
ii. 8.31 L kPa
Why is NaCl(s) harder to melt compared to H2O(s)?
NaCl only has ionic bonds, which are strong - during the melting process, the ionic bonds are disrupted, thus more energy is required to break the bonds
Ice is a molecular compound held by hydrogen bonds - hydrogen bonds require less energy to break compared to ionic bonds (note that the covalent compounds are not broken since it is the weaker bonds that are disrupted first)
Why do Cl, Br, and I all have different states at rtp despite being in the same group
Size of dispersion force correlates to dispersion force - Cl has the weakest dispersion force thus I has highest melting
larger electron cloud = stronger dispersion force
What is meant by gas pressure?
The collisions molecules have with the walls of the container
What is Boyle’s Law?
For a fixed amount of gas at a constant temp, pressure is inversely proportional to volume
What is Charle’s Law?
For a fixed amount of gas at constant pressure, volume is directly proportional to temp
What are the 2 types of solids?
Crystalline and amorphous
What are the 4 types of crystallin solids?
- ionic solids - consists of charged particles, high melting point and conduct electricity only when molten or aq
- metallic solids - metal cat in a sea of electrons, wide range of m.p., conduct in all states
- covalent network solids - 3D structures containing large amounts of atoms, ex high m.p., cannot conduct (lack ions)
- molecular solids - molecules held tgt by weak imf, low m.p., poor or don’t conduct (no free ions)
What bonds are in a
a. polar molecule
b. non-polar molecule
a. hydrogen bonds and dipole bonds
b. dispersion forces
What is needed for a liquid to escape to a gas?
Enough energy to overcome imf (H bonds in H2O)
What is the enhalpy of vaporisation and what does it depend on?
∆Hvap = heat needed to break the bond
depend on atomic size (HF > HBr)
What is vapour pressure dependent on?
- Dependent on temperature, high temp = more collisions = more pressure
- Dependent on imf, strong imf = low vapour pressure (stronger imf = more tightly packed
What is viscosity?
The resistance to flow (thiccness), stronger imf = more viscosity
What is surface tension?
Energy required to increase surface area to allow interior liquid molecules to move to the surface
What is Dalton’s Law of Partial Pressures?
Ptotal = P1 + P2 + P3…
He or Xe, which diffuses faster?
He
What is the combined gas law?
P1V1/T1 = P2V2/T2
A sample of oxygen gas has a volume of 425 mL when the pressure is equal to 387 kPa. The gas is allowed to expand into a 1.75 L container. Calculate the new pressure of the gas.
94.0 kPa
What is the ideal gas law?
pV = nRT
What volume is occupied by 3.76 g of oxygen gas at a pressure of 88.4 kPa and a temperature of 19°C
- rmb that its O2, not O
3.23 L
What is the enthalpy of a solution?
ΔHsoln = ΔH1 + ΔH2 + ΔH3
Will ethanol (CH3CH2OH) dissolve in water (H2O)?
Yes. The H bonds in ethanol has enough energy to break the H bonds in water
Will hexane (C6H14) mix with water?
No. Hexane is non-polar and only has dispersion forces which cannot overcome the H bonds in H2O
Why is KMnO3 soluble in H2O but not C6H14?
KMnO3 has ion-dipole bonds that can break the H bonds in H2O, but C6H14 is non-polar and only has dispersion forces so it’s too weak to break the H bonds in H2O
In an equilibrium concentration-time graph, does the product start at the bottom or the top?
Product = bottom
Reactant = top
Initially, a mixture of 0.100 M NO, 0.050 M H2 and 0.100 M H2O was allowed to reach equilibrium at a temperature, T°C. There was no N2 present initially. At equilibrium, the concentration of NO was found to be 0.062 M. Calculate Kc for the reaction represented by the following equation:
2NO(g) + 2H2(g) ⇌ N2(g) + 2H2O(g)
- use ICE
- rmb s.f.
6.5 x 10^2
What happens when:
Qc > Kc
Qc < Kc
Qc = Kc
- more Qc = products, more Kc = products
Qc > Kc = products favoured
Qc < Kc = reactants favoured
Qc = Kc = equilibrium
At a given temperature, a chemical reaction represented by the following equation:
CO(g)+H2O(g) ⇌ H2(g) + CO2(g), where Kc = 1.34. If the system has the following initial concentrations, is it at equilibrium? If not, in which direction must the reaction proceed to reach equilibrium?
[CO]=0.100 M; [H2O]=0.100 M; [H2]=0.100 M; [CO2]=0.100 M.
- find Qc (same formula as Kc)
- determine equilibrium
Qc = 1.00
Qc < Kc, so equilibrium favours reactants, reaction needs to go forward to reach equilibrium
What would happen if you changed the conditions by increasing the concentration of A?
A(g) + 2B(g) ⇌ C(g) + D(g)
Concentration relates to the amount of particles in a substance, if the concentration of A is increased, then, as per Le Chatelier’s principle, the system will more the reaction forward to decrease the concentration of A and produce more C and D
What would happen if you changed the conditions by increasing the pressure by a decrease in volume of the vessel?
A(g) + 2B(g) ⇌ C(g) + D(g)
Pressure is created when particles hit the ‘wall’. According to Le Chatelier’s principle, the system will decrease the pressure by decreasing the number of particles. Since the reactants have moer particles (3:2), there will be a forward reaction
A(g) + 2B(g) ⇌ C(g) + D(g) ΔH = -ve
What would happen if you changed the conditions by increasing the temperature?
Since the reaction is exothermic, as per Le Chatelier’s principle, the reaction will reverse to counteract with the change. Kc will decrease
A(g) + 2B(g) ⇌ C(g) + D(g)
What would happen if a catalyst is added to the system?
A catalyst will speed up both the forward and reverse reaction, thus will contribute to no change
What happens to a solution of PbCl2 when 0.010 M of NaCl is added?
According to Le Chatelier, the system will want to decrease the concentration of Cl:
PbCl2 –> Pb+ + 2Cl-
The reaction then reverses to decrease the amount of Cl
What is an:
a. Arrhenius acid and base
b. Bronsted-Lowry acid and base
c. Lewis acid and base
a. a = H+, b = OH-
b. a = proton donors, b = proton acceptors
c. a = electron acceptors, b = electron donors
How much energy is required to convert 2.0 mol of ethanol (CH2CH2OH) from a solid to a liquid at its normal melting point?
ΔHfus = + 4.9 kJ mol−1
1 mol = 4.9 kJ mol−1
2 mol = 9.8 kJ mol−1
How much energy is required to convert 75 g of water to water vapour at its normal boiling point?
ΔHfus = + 40.8 kJ mol−1
- find mol
- multiply mol with ΔHfus
1.7 x 10^2
1.00 x 102 mL of an 0.0100 M aqueous solution of calcium hydroxide will absorb carbon dioxide according to the equation
Ca(OH)2(aq) + 2CO2(g) → Ca(HCO3)2(aq)
The maximum volume, in mL, at 1.00 atm and 0°C of CO2 that could be absorbed by the solution is
- find n(CO2) by finding n(Ca(HCO3)2)
- use pV = nRT
- change L to mL
44.8mL
The molar volume of oxygen, in L, at 1.00 atm and 100°C, is
a. 24.5
b. 30.6
c. 22.4
d. 8.2
- find n/V
b. 30.6
What bonds are broken when KNO3 is dissolved in water?
a. dispersion forces only
b. ionic bonds
c. ionic bonds and covalent bonds
d. covalent bonds
b. ionic bonds
C2H4 (g) + 2H2O (g) ⇌ C2H5OH(g)
Kc = 9.0 x 103 at 600 K
What is the value of Kc for the chemical reaction described by the equation below?
C2H5OH(g) ⇌ C2H4 (g) + 2H2O (g)
(T = 600K)
- to reverse, 1/k
1.1 x 10–4
3.0 mol of SO2 and 2.0 mol of O2 are made to come to equilibrium in a 5.0 L container according to the equation:
2SO2(g) + O2(g) ⇌ 2SO3(g)
At equilibrium the concentration of SO2 is found to be 0.40 M. At this temperature, what is the value of the equilibrium constant?
- rmb squares
0.83
What is the conjugate base of CH3COOH?
CH3COO-
HCO3-, HSO4-, HS-, HPO42- and H2PO43- are examples of what?
Amphoteric
What are polyprotic acids?
Acids that can donate more than 1 proton
In pure water at 5°C the hydroxide ion concentration is measured to be 4.0 × 10–8 M. What is the Kw and pH of pure water at this temperature?
a. Kw = 1.6 × 10–15 and pH = 7.4
b. Kw = 1.0 × 10–14 and pH = 6.6
c. Kw = 1.0 × 10–14 and pH = 7.0
d. Kw = 1.6 × 10–15 and pH = 7.0
- higher temp = higher Kw = pH decrease
- rmb that Kw is the temp at 25 degrees
a. Kw = 1.6 × 10–15 and pH = 7.4
The pH of a 0.090 M solution of the weak acid nitrous acid was measured to be 2.20. What is the [H+]?
- 10^-pH
6.3 x 10^-3
What is the pH at 25°C of a 0.0050 M solution of Ba(OH)2?
- Barium hydroxide dissociates into 2 hydroxide ions
- 2 x 0.005, then continue
pH = 12
Nitrous acid ionises in water according to the following equation:
HNO2(aq) + H2O(l) ⇌ H3O+(aq) + NO2–(aq)
Which one of the following is correct when 450 mL of water is added to a 50 mL solution of nitrous acid at constant temperature.
a. [H3O+] in the solution increases
b. Ka of the acid decreases
c. pH of the solution increases
d. Ka of the acid increases
- [H3O+] decreases (diluted)
- Ka is only affected by temperature
c. pH of solution increases
100 mL of a 0.010 M solution of barium hydroxide (Ba(OH)2) is diluted by adding 900 mL of water at 25°C. The pH of the resulting solution will be
- find the mol of barium hydroxide
- dilution = 0.002/(0.9+0.1) = 0.002
- find pOH
- find pH
pH = 11.3
What volume will 4.91 x 1022 atoms of helium occupy at 1.00 atm and 273K?
- convert atoms to mol (atom / avocado)
- pV = nRT
How much energy is released when 1.25g of NaF changes from liquid to solid at melting point, ∆Hfus = 29.3 kJ mol^-1
- find n
- n x ∆Hfus
-0.87 kJ
100 mL of 0.10 M NaOH and 100 mL of 0.20 M HCl are mixed. What is the pH of the resulting solution?
- find n of NaOH and HCl
- determine limiting reactant
- total solution = 0.1 + 0.1
- find [H+] = c = n/V
- find pH
1.3
Gaseous NOCl decomposes to form the gases NO and Cl2 according to the following equilibrium.
2NOCl(g) ⇌ 2NO(g) + Cl2(g) Kc = 1.6 × 10–5 at 35 °C.
What is the value of the equilibrium constant, at 35 °C, for the following equilibrium?
NO(g) + ½Cl2(g) ⇌ NOCl(g)
a. 6.3 × 10 4
b. 1.6 × 10 –5
c. –1.6 × 10–5
d. 2.5 × 10 2
- to half = sqrtk
- to reverse = 1/k
c. –1.6 × 10–5
