Calculating K For Overall Reaction - Video Tutorials & Practice Problems
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Chemical reactions often occur in multiple steps, each with its own equilibrium constant. To calculate the equilibrium constant (Keq) for the overall reaction, you must consider the equilibrium constants of the individual steps. The process involves locating each compound from the overall reaction within the partial reactions, ensuring they match in number and phase. If a compound appears in multiple reactions, skip it. You may need to reverse or multiply the partial reactions, affecting the equilibrium constant. After aligning the reactions correctly, combine them, canceling out intermediates—compounds that appear as both reactants and products. The overall Keq is then found by multiplying the constants of the partial reactions. This method ensures the accurate determination of the equilibrium constant for complex reactions, which is crucial for predicting the reaction's behavior and understanding chemical kinetics and thermodynamics.
Calculating Keq of the Overall Reaction
Video transcript
Calculate Kc for: C(s) + ½ O2(g) + H2(g) ⇌ ½ CH3OH(g) + ½ CO(g) Kc = ?
Given the following reactions:
4 C(s) + 2 O2(g) ⇌ 4 CO(g) Kp = 2.11 x 1043
CH3OH(g) + H2O(g) ⇌ CO2(g) + 3 H2(g) Kp = 7.17 x 10–2
CO(g) + H2O(g) ⇌ CO2(g) + H2(g) Kp = 2.00 x 103
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More setsHere’s what students ask on this topic:
When we add two reactions together, how can we determine the value of the equilibrium constant for the new reaction?
When you add two chemical reactions together to form a new reaction, the equilibrium constant for the new reaction can be determined by multiplying the equilibrium constants of the original reactions. This is because the equilibrium constant, denoted as K, is a reflection of the ratio of the concentrations of the products to reactants, each raised to the power of their stoichiometric coefficients.
For example, if you have two reactions:
- A → B with equilibrium constant K1
- B → C with equilibrium constant K2
And you add them to get the new reaction:
A → C
The equilibrium constant for this new reaction, K3, is the product of K1 and K2:
K3 = K1 * K2
This relationship holds because the equilibrium constant is derived from the rate constants of the forward and reverse reactions, and when reactions are added, their rate constants multiply in a way that leads to the multiplication of their equilibrium constants. Remember, this only applies if the reactions are added in such a way that intermediates like B in this example are the same (i.e., they cancel out).
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The table above provides the Keq values for two reactions. What is the correct mathematical expression needed to determine the equilibrium constant of the reaction shown below?
To answer your question, I need to clarify that the table mentioned is not visible in your query. However, I can guide you on how to determine the equilibrium constant (Keq) for a given reaction using the Keq values of other reactions.
If you have two reactions:
- A -> B with Keq = Keq1
- C -> D with Keq = Keq2
And you want to determine the Keq for a new reaction that is a combination of the two, such as:
A + C -> B + D
You would use the following mathematical expression:
This is because the equilibrium constants of individual reactions multiply when reactions are added together.
If the new reaction is the reverse of one of the given reactions, you would take the reciprocal of the Keq value for that reaction. If the stoichiometry of a reaction is multiplied by a coefficient, you would raise the Keq to the power of that coefficient.
For example, if the new reaction is the reverse of Reaction 1, the expression would be:
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