GRE Subject Test: Chemistry : Reaction Chemistry

Study concepts, example questions & explanations for GRE Subject Test: Chemistry

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Example Questions

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Example Question #1 : Reaction Equilibrium


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Based on the equilibrium reaction shown, how would adding  to the system affect the equilibrium?

Possible Answers:

Adding  would not have any effect on the equilibrium

Adding  to the system would cause the equilibrium to shift to the right, producing more  in order to reduce the concentration of 

The effect of adding  to the system cannot be predicted

Adding  to the system would cause the equilibrium to shift to the right, producing more  in order to reduce the concentration of 

Adding  to the system would cause the equilibrium to shift to the left, producing more  in order to reduce the concentration of 

Correct answer:

Adding  to the system would cause the equilibrium to shift to the right, producing more  in order to reduce the concentration of 

Explanation:

According to Le Chatelier's principle, if an equilibrium reaction is disturbed by addition of a reactant or product, the equilibrium will shift to counteract the disturbance. Therefore, adding  to the system would cause the equilibrium to shift to the right, producing more  in order to reduce the concentration of .

Example Question #31 : Reaction Chemistry

Which method can be used to decrease the activation energy of a reaction?

Possible Answers:

Increasing the pressure

Increasing the temperature

Increasing the concentration of reactants

All of these

Adding a catalyst

Correct answer:

All of these

Explanation:

The activation energy is the minimum amount of energy required to start a chemical reaction. Based on the collision model, increasing the temperature, pressure, and concentration for a chemical reaction will decrease the activation energy. This is because increasing these factors increases the number of collisions of molecules. Molecules must collide to react.

Example Question #1 : Equilibrium Constant And Reaction Quotient

Which of the following is true regarding the solubility product constant, , for a reaction in the form:

Possible Answers:

 has units of moles per liter

The concentration of substance  strongly influences the value of 

 represents the ratio of reactants to products as the reaction progresses

As more of substance  dissolves in the given solution, increases

Correct answer:

Explanation:

To determine the solubility product constant, we only need the concentrations and coefficients of the ions. The effective concentration of any pure substance (solid, liquid, or gas) is equal to one by definition, so does not influence the value of . The equation for the solubility product constant of this reaction is:

The units of the solubility product constant will depend on the coefficients of the products. will be a constant for the reaction, and will not change as more solid dissolves or as the reaction progresses.

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