18 Questions
What is the equilibrium constant for the reaction PCl5(g) ⇌ PCl3(g) + Cl2(g) if the flask at equilibrium contains 0.1 mol PCl5, 0.20 mol PCl3, and 0.20 mol Cl2?
0.02
Which compound is NOT a Brønsted-Lowry acid?
NH3
In the reaction 2 CO2(g) ⇌ 2 CO(g) + O2(g), how can the equilibrium partial pressure of CO (g) be maximized according to Le Châtelier's principle?
At high temperature and low pressure
A 0.045 M aqueous solution with a pOH of 5.33 is classified as:
weak base
For a system that absorbs 60 J of heat while 40 J of work are performed on it, then releases 30 J of heat while doing 70 J of work, what is the change in internal energy (ΔU)?
30 J
Which statement is TRUE about enthalpy?
Enthalpy is a state function.
What is the heat capacity of the water in the bomb calorimeter?
4.18 J oC−1 g−1
Which substance has the highest standard enthalpy of formation among NH3(g), HCl(g), and NH4Cl(s)?
HCl(g)
What is the equilibrium constant for the reaction NH3(g) + HCl(g) ⇌ NH4Cl(s) at 25oC?
1.39
In Le Chatelier's principle, what happens when a stress is applied to a system at equilibrium?
The system shifts to relieve the stress and re-establish equilibrium.
Which concept involves ions that do not participate in a chemical reaction but are present in the solution?
Spectator ions
What is the rest mass of a neutron?
1.675 x 1027 kg
Which of the following statements about enthalpy is correct?
H is the value of q measured under conditions of constant pressure.
For the reaction N2O4(g) + Cl2(g) → 2 NOCl(g) + O2(g), what is ΔHo?
+222.09 kJ mol-1
In the reaction 2 KCl(aq) + O2(g) → 2 KClO3(aq), which species acts as a spectator ion?
KCl(aq)
Which of the following reactions has ΔH equal to ΔH°f?
128 kJ
If a human needs 11300 kJ of energy per day, and ΔHcombustion of glucose is -5650 kJ mol–1, how many grams of glucose must be consumed per day?
200 g
What is the specific heat capacity of lead if 52 J of heat raises the temperature of a block of lead from 22°C to 32°C?
0.115 J g-1 K-1
Study Notes
Le Châtelier's Principle
- Le Châtelier's principle predicts that the equilibrium partial pressure of CO (g) can be maximised under different conditions:
- Low temperature and low pressure
- High temperature and low pressure
- High temperature and high pressure
- Low temperature and high pressure
- In the presence of solid carbon
Equilibrium Constant
- The equilibrium constant (Kc) can be calculated from the concentrations of reactants and products at equilibrium:
- Kc = [PCl3]^2 [Cl2]^2 / [PCl5]^2
Thermodynamics
- ΔU (change in internal energy) can be calculated from the heat absorbed and work done on the system:
- ΔU = Q - W
- Enthalpy (H) is a state function, and ΔH is independent of the state of the reactants and products:
- ΔH = ΔH°f (enthalpy of formation)
Calorimetry
- The heat of combustion of octane (C8H18) can be calculated from the temperature change in a bomb calorimeter:
- ΔHcombustion = -5650 kJ mol-1 (for glucose)
Reaction Equilibria
- The equilibrium constant (Kc) can be calculated from the concentrations of reactants and products at equilibrium:
- Kc = [NH4Cl] / [NH3] [HCl]
- The reaction quotient (Q) can be calculated from the concentrations of reactants and products at any time:
- Q = [NH4Cl] / [NH3] [HCl]
Thermodynamic Properties
- Standard enthalpy of formation (ΔH°f) is the enthalpy change for the formation of one mole of a substance from its constituent elements:
- ΔH°f (NH3) = -46.19 kJ mol-1
- ΔH°f (HCl) = -92.30 kJ mol-1
- ΔH°f (NH4Cl) = -314.4 kJ mol-1
Energy Requirements
- A human being requires 11300 kJ of energy per day:
- To satisfy this energy requirement, a person needs to consume a certain amount of glucose:
- Amount of glucose = 11300 kJ / -5650 kJ mol-1 = 2 mol (approx.)
- To satisfy this energy requirement, a person needs to consume a certain amount of glucose:
Test your understanding of Le Châtelier's principle with this quiz, focusing on predicting equilibrium conditions for a given reaction. Explore how different factors impact the equilibrium partial pressure of carbon monoxide gas in the reaction 2 CO2(g) ⇌ 2 CO(g) + O2(g).
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