High School Chemistry : Equilibrium

Study concepts, example questions & explanations for High School Chemistry

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Example Questions

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Example Question #1 : Identifying Reaction Equilibrium

Consider the following balanced reaction:

When the reaction is at equilibrium, which of the following actions will result in more products?

Possible Answers:

Lower the temperature

Increase temperature

Remove hydrogen gas

Remove nitrogen gas

Correct answer:

Lower the temperature

Explanation:

Le Chatelier's principle states that a system will shift in a particular direction in order to reduce introduced stress to the system. In other words, if something is added to one side of the equation, the other side will consequently increase in order to restore equilibrium.

The above reaction is exothermic, meaning that heat is released from the system. As a result, heat is considered a product.

By removing nitrogen or hydrogen gas, the system would shift to the left in order to create more reactants. If temperature is decreased, the system will create more heat by shifting to the right. Not only will this create more heat, but it will also create more ammonia, as they are both products of the reaction.

Example Question #1 : Identifying Reaction Equilibrium

Consider the following generic reaction:

If the equilibrium concentration of  is 1M, what is the equilibrium concentration of ?

Possible Answers:

Correct answer:

Explanation:

We can set up the equilibrium expression by placing the products, raised to the power of their coefficients, in the numerator and reactants, raised to the power of their coefficients, in the denominator:

We are given the value of the equilibrium constant and the equilibrium concentration of . Using stoichiometric coefficients, we can determine that a variable concentration, , of  will be present at equilibrium, and  of  will be present at equilibrium. Plugging in:

Simplify:

Now we can solve for  (which is the equilibrium concentration of , as we assigned) by dividing both sides by 4 and then taking the cube root.

Rounding to 2 sig figs (to match the two numbers we were given by the problem), we get:

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