Podcast
Questions and Answers
In the equilibrium calculation process, what does the 'change in concentration' row typically represent?
In the equilibrium calculation process, what does the 'change in concentration' row typically represent?
- A factor of 'x' based on the reaction's stoichiometry. (correct)
- The equilibrium constant, K, for the reaction.
- The actual concentrations at equilibrium.
- The initial concentrations of reactants.
When solving for 'x' in an equilibrium problem using the quadratic formula, how should you handle multiple solutions for 'x'?
When solving for 'x' in an equilibrium problem using the quadratic formula, how should you handle multiple solutions for 'x'?
- Use the smallest positive value.
- Use the largest positive value.
- Average the solutions to find the most accurate value.
- Reject any solutions that result in physically impossible (e.g., negative) concentrations. (correct)
For the reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$, if the volume of the container is decreased, how will the equilibrium shift?
For the reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$, if the volume of the container is decreased, how will the equilibrium shift?
- The reaction will stop.
- Shift to the left, favoring the reactants.
- No shift will occur.
- Shift to the right, favoring the products. (correct)
Consider the endothermic reaction: $A(g) \rightleftharpoons B(g) + C(g)$. What effect will increasing the temperature have on the equilibrium constant (K)?
Consider the endothermic reaction: $A(g) \rightleftharpoons B(g) + C(g)$. What effect will increasing the temperature have on the equilibrium constant (K)?
How do catalysts affect chemical equilibria?
How do catalysts affect chemical equilibria?
If a system at equilibrium is disturbed, which principle is used to predict the shift in the equilibrium position?
If a system at equilibrium is disturbed, which principle is used to predict the shift in the equilibrium position?
For the reaction $2A(g) \rightleftharpoons B(g)$, what effect does increasing the pressure (by decreasing the volume) have on the equilibrium?
For the reaction $2A(g) \rightleftharpoons B(g)$, what effect does increasing the pressure (by decreasing the volume) have on the equilibrium?
Which of the following, when changed, will alter the value of the equilibrium constant, K?
Which of the following, when changed, will alter the value of the equilibrium constant, K?
For an exothermic reaction, how does decreasing the temperature affect the equilibrium?
For an exothermic reaction, how does decreasing the temperature affect the equilibrium?
Consider the gas-phase reaction: $A + B \rightleftharpoons C$. If adding more of reactant A to the system increases the amount of C formed, what happens to the equilibrium?
Consider the gas-phase reaction: $A + B \rightleftharpoons C$. If adding more of reactant A to the system increases the amount of C formed, what happens to the equilibrium?
In the reaction $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$, what happens to the equilibrium if an inert gas is added at constant volume?
In the reaction $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$, what happens to the equilibrium if an inert gas is added at constant volume?
For the endothermic reaction $X(g) \rightleftharpoons Y(g) + Z(g)$, which change will NOT shift the equilibrium to the right?
For the endothermic reaction $X(g) \rightleftharpoons Y(g) + Z(g)$, which change will NOT shift the equilibrium to the right?
For a reaction at equilibrium, if the forward reaction is endothermic, what effect will cooling the reaction have on the concentration of products?
For a reaction at equilibrium, if the forward reaction is endothermic, what effect will cooling the reaction have on the concentration of products?
What is the primary effect of a catalyst on a reversible reaction at equilibrium?
What is the primary effect of a catalyst on a reversible reaction at equilibrium?
Consider the following equilibrium: $A(g) + B(s) \rightleftharpoons C(g)$. If the partial pressure of A is increased, what will happen to the amount of solid B?
Consider the following equilibrium: $A(g) + B(s) \rightleftharpoons C(g)$. If the partial pressure of A is increased, what will happen to the amount of solid B?
Which of the following changes will affect the equilibrium constant ($K$) for the synthesis of ammonia ($N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$)?
Which of the following changes will affect the equilibrium constant ($K$) for the synthesis of ammonia ($N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$)?
For a gas-phase reaction, if increasing the volume of the container shifts the equilibrium towards the product side, what can be concluded about the number of moles of gas?
For a gas-phase reaction, if increasing the volume of the container shifts the equilibrium towards the product side, what can be concluded about the number of moles of gas?
In an exothermic reaction, if you increase the temperature, what happens to the equilibrium constant, K?
In an exothermic reaction, if you increase the temperature, what happens to the equilibrium constant, K?
Consider the reaction $A(g) + B(g) \rightleftharpoons 2C(g)$. If the reaction is started with only A and B, and at equilibrium, it is found that the partial pressures of A, B, and C are all equal, what can be said about the equilibrium constant Kp?
Consider the reaction $A(g) + B(g) \rightleftharpoons 2C(g)$. If the reaction is started with only A and B, and at equilibrium, it is found that the partial pressures of A, B, and C are all equal, what can be said about the equilibrium constant Kp?
If a reaction is endothermic, how does decreasing the temperature affect both the equilibrium and the equilibrium constant?
If a reaction is endothermic, how does decreasing the temperature affect both the equilibrium and the equilibrium constant?
For the equilibrium reaction $H_2(g) + I_2(g) \rightleftharpoons 2HI(g)$, if more $H_2(g)$ is added to the system, what will happen to the concentration of $I_2(g)$ at the new equilibrium?
For the equilibrium reaction $H_2(g) + I_2(g) \rightleftharpoons 2HI(g)$, if more $H_2(g)$ is added to the system, what will happen to the concentration of $I_2(g)$ at the new equilibrium?
Which of the following is true regarding the effect of an inert gas on a reaction at equilibrium in a closed system at constant pressure?
Which of the following is true regarding the effect of an inert gas on a reaction at equilibrium in a closed system at constant pressure?
Consider the equilibrium: $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$. If the volume of the reaction vessel is increased, how will the equilibrium shift?
Consider the equilibrium: $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$. If the volume of the reaction vessel is increased, how will the equilibrium shift?
If the reaction $A(g) \rightleftharpoons B(g)$ has an equilibrium constant K much less than 1, and heat is added, how will the concentrations change if the reaction is exothermic?
If the reaction $A(g) \rightleftharpoons B(g)$ has an equilibrium constant K much less than 1, and heat is added, how will the concentrations change if the reaction is exothermic?
Which of the following statements accurately describes the effect of a catalyst on an endothermic reaction at equilibrium?
Which of the following statements accurately describes the effect of a catalyst on an endothermic reaction at equilibrium?
Flashcards
Calculating Equilibrium Concentrations
Calculating Equilibrium Concentrations
Equilibrium concentrations can be found from initial concentrations and changes based on stoichiometry, using the equilibrium constant.
Change in concentration
Change in concentration
Change in concentration during a reaction will be a factor of 'x' based on stoichiometry
Le Châtelier's Principle
Le Châtelier's Principle
It states that if a system at equilibrium is disturbed, it will shift to counteract the disturbance.
Adding a reaction component
Adding a reaction component
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Removing a reaction component
Removing a reaction component
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Volume/Pressure Change
Volume/Pressure Change
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Endothermic and Heat
Endothermic and Heat
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Exothermic and Heat
Exothermic and Heat
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Catalysts
Catalysts
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Catalyst and Equilibrium
Catalyst and Equilibrium
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Study Notes
Calculating Equilibrium Concentrations
- Equilibrium concentrations can be derived from the equilibrium constant, initial concentrations, and stoichiometric changes.
- Set-up a table to determine equilibrium concentration, the "change in concentration" row relates to "x" based on the stoichiometry.
Example Problem
- A 1.000 L flask contains 1.000 mol of H2(g) and 2.000 mol of I2(g) at 448 °C.
- The equilibrium constant K is 50.5 at 448 °C.
- The goal is to find the equilibrium concentrations of H2, I2, and HI.
Solution
- Write the balanced equilibrium equation: H2(g) + I2(g) ⇌ 2 HI(g)
- Set up the table (ICE table)
- Initial concentrations: [H2] = 1.000 M, [I2] = 2.000 M, [HI] = 0 M
- Change in concetrations: [H2] = -x, [I2] = -x, [HI] = +2x
- Equilibrium concentrations: [H2] = 1.000 - x, [I2] = 2.000 - x, [HI] = 2x
- Write and solve for the equilibrium constant expression.
- Kc = [HI]^2 / [H2][I2] = (2x)^2 / (1.000 - x)(2.000 - x) = 50.5
- Solve for x using the quadratic formula, resulting in x = 2.323 or 0.935.
- Choose the physically sensible x value.
- Since subtracting x from 1.000 M must yield a positive value, x = 0.935 M.
- Calculate the equilibrium concentrations.
- [H2]eq = 1.000 - 0.935 = 0.065 M
- [I2]eq = 2.000 - 0.935 = 1.065 M
- [HI]eq = 2(0.935) = 1.87 M
Key takeaway
- One of the solutions to the quadratic formula will give a value that leads to a chemically impossible negative concentration, hence reject this solution.
LeChâtelier's Principle
- If a system at equilibrium is disturbed by a change in temperature, pressure, or component concentration, the system will shift its equilibrium position to counteract the disturbance.
Changing Conditions and Equilibrium Shifts
- LeChâtelier's Principle predicts shifts in equilibrium based on changes in conditions
- Concentration: Adding a substance shifts the equilibrium to consume it, while removing a substance shifts the equilibrium to produce it.
- Pressure: Reducing volume (increasing pressure) shifts the equilibrium towards fewer moles of gas.
- Temperature:
- Increasing temperature shifts the equilibrium as if heat were added as a reactant for endothermic reactions or as a product for exothermic reactions.
- This causes a shift away from the side where heat is effectively added.
Change in Reactant/Product Concentration
- Adding a reaction component causes the system to use up some of it.
- Removing a reaction component causes the system to produce more of it.
Change in Volume/Pressure
- Gas equilibrium is affected by pressure or volume changes.
- Higher volume/lower pressure favors the side with more moles of gas, and vice versa.
Change in Temperature
- Endothermic reactions treat heat like a reactant; adding heat shifts the reaction toward products.
- Exothermic reactions treat heat like a product; adding heat shifts the reaction toward reactants.
Catalysts
- Catalysts increase the rate of both forward and reverse reactions equally.
- Equilibrium is reached faster, but the equilibrium composition remains unchanged.
- Activation energy is lowered, allowing equilibrium at lower temperatures.
Using Le Châtelier's Principle: Predicting Shifts
- N2O4(g) ⇌ 2 NO2(g), ΔH° = 58.0 kJ:
- Adding N2O4 shifts the equilibrium to the right (products).
- Removing NO2 shifts the equilibrium to the right (products).
- Adding N2 (inert gas) has no effect on the equilibrium position.
- Increasing volume shifts the equilibrium to the right (more gas molecules).
- Decreasing temperature shifts the equilibrium to the left (reactants), since reaction is endothermic.
Predicting Effect of Temperature on K
- Reaction: N2(g) + 3H2(g) ⇌ 2 NH3(g)
- The reaction is exothermic, and the forward direction generates heat.
- Increasing temperature causes the reaction to shift toward less NH3 and more N2 and H2.
- The effect can be seen by the values ​​for K, which become larger at lower temperatures.
Thermodynamic Considerations
- Using standard enthalpies of formation (ΔHf°) at 25 °C:
- ΔHf° values for elements in their normal states (e.g., H2(g), N2(g)) are zero.
- For NH3(g), ΔHf° = -46.19 kJ/mol.
- The total enthalpy change is: (2 mol)(-46.19 kJ/mol) - 0 = -92.38 kJ
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