Chapter 15: Problem 78
An equilibrium mixture of \(\mathrm{SO}_{3}, \mathrm{SO}_{2}\), and \(\mathrm{O}_{2}\) at \(727^{\circ} \mathrm{C}\) is \(0.0160 \mathrm{MSO}_{3}, 0.0056 \mathrm{M} \mathrm{SO}_{2}\), and \(0.0021 \mathrm{M} \mathrm{O}_{2} .\) What is the value of \(K_{c}\) for the following reaction? $$ \mathrm{SO}_{2}(g)+\frac{1}{2} \mathrm{O}_{2}(g) \rightleftharpoons \mathrm{SO}_{3}(g) $$
Short Answer
Step by step solution
Write the Expression for Equilibrium Constant
Substitute the Equilibrium Concentrations into the Expression
Calculate the Value of Kc
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Chemical Equilibrium
For example, in the reaction between sulfur dioxide (\(\text{SO}_2\)) and oxygen (\(\text{O}_2\)) to form sulfur trioxide (\(\text{SO}_3\)), equilibrium is reached when the number of \(\text{SO}_3\) molecules being formed equals the number being decomposed back into \(\text{SO}_2\) and \(\text{O}_2\).
- Concentrations remain constant, but bonds are continuously being broken and formed.
- The system is dynamic, not static, representing a continuous interaction at the molecular level.
- Conditions like pressure and temperature can affect the position of equilibrium.
Reaction Quotient
To compute \(Q\), you use the same expression as for \(K_c\): \[ Q = \frac{[\text{SO}_3]}{[\text{SO}_2][\text{O}_2]^{1/2}} \]where the concentrations employed are from any point in the reaction.
- If \(Q < K_c\), the reaction will proceed forward, forming more products to reach equilibrium.
- If \(Q > K_c\), the reaction moves backwards, producing more reactants until equilibrium is established.
- When \(Q = K_c\), the system is at equilibrium, and no shift occurs.
Equilibrium Concentrations
In the given exercise, the specific equilibrium concentrations were:
- \([\text{SO}_3] = 0.0160\, \text{M}\)
- \([\text{SO}_2] = 0.0056\, \text{M}\)
- \([\text{O}_2] = 0.0021\, \text{M}\)
Le Chatelier's Principle
Some practical ways this principle works include:
- Increasing the concentration of a reactant will shift the equilibrium towards the products.
- Raising the temperature typically shifts equilibrium in the endothermic direction. For an exothermic reaction, it pushes the equilibrium towards the reactants.
- Changing the pressure affects gaseous reactions. Increasing pressure shifts equilibrium towards the side with fewer moles.