Chemical Reactions

Standardized Test PrepChemical Reactions

Chemical Reactions

Preview• Understanding Concepts • Reading Skills• Interpreting Graphics


Understanding Concepts

1. What type of reaction is Pb(NO3)2 + 2KI → PbI2 + 2KNO3?

A. a synthesis reaction

B. a combustion reaction

C. a decomposition reaction

D. a double-displacement reaction


Understanding Concepts, continued

1. What type of reaction is Pb(NO3)2 + 2KI → PbI2 + 2KNO3?


B. a combustion reaction

C. a decomposition reaction




2. Which of the following describes an endothermic chemical reaction?

F. the explosion of fireworks in the sky

G. photosynthesis in plant cells

H. respiration in animal cells

I. the burning of wood in a fireplace



2. Which of the following describes an endothermic chemical reaction?

F. the explosion of fireworks in the sky

G. photosynthesis in plant cells

H. respiration in animal cells

I. the burning of wood in a fireplace



3. Which of the following changes will always increase the rate of a chemical reaction?

A. lowering the temperature

B. adding an inhibitor to the reaction mixture

C. increasing the concentration of the reactants

D. decreasing the surface area of the reactants



3. Which of the following changes will always increase the rate of a chemical reaction?

A. lowering the temperature

B. adding an inhibitor to the reaction mixture

C. increasing the concentration of the reactants

D. decreasing the surface area of the reactants


Understanding Concepts, continued4. The equation PCl3 + Cl2 PCl⇆ 5 + energy describes an

equilibrium system. How would raising the temperature affect the system?

F. The equilibrium would move to the right to create more PCl3 and Cl2.

G. The equilibrium would move to the left to create more PCl3 and Cl2.

H. The equilibrium would move to the right to create more PCl5.

I. The equilibrium would move to the left to create more PCl5.

















5. In the redox reaction H2 + F2 → 2HF, which element is reduced, and which is oxidized?



5. In the redox reaction H2 + F2 → 2HF, which element is reduced, and which is oxidized?

Answer: F is reduced and H is oxidized.


Reading Skills

NITROGEN FIXATION

The element nitrogen makes up about 78% of Earth’s atmosphere. It is also an essential component of many of the chemical compounds that are vital to all living things. However, atmospheric nitrogen is not directly accessible to living things; it is primarily in the form of N2, a molecule composed of two atoms of nitrogen linked by a triple bond. Because of the strength of this bond, large amounts of energy are required to free up the nitrogen atoms so that they can become part of the organic molecules of life.


Reading Skills, continued

NITROGEN FIXATION, continued

When sufficient energy is added to N2 and hydrogen is present in the form of H2, the result is the compound ammonia, NH3. The nitrogen in ammonia is much more reactive than that in N2 and thus is much more readily available to living systems. The process of combining nitrogen and hydrogen into ammonia is an oxidation-reduction reaction known as nitrogen fixation. Nitrogen fixation is accomplished by certain microorganisms, which then feed nitrogen-rich compounds into the rest of the ecosystem. Nitrogen fixation is also done artificially at chemical plants where ammonia is made.



6. In addition to being an oxidation-reduction reaction, what type of reaction is nitrogen fixation of N2 and H2 into NH3?


B. a decomposition reaction

C. a single-displacement reaction




6. In addition to being an oxidation-reduction reaction, what type of reaction is nitrogen fixation of N2 and H2 into NH3?


B. a decomposition reaction

C. a single-displacement reaction




7. Write the balanced chemical equation for nitrogen fixation.



7. Write the balanced chemical equation for nitrogen fixation.

Answer: N2 + 3H2 → 2NH3


Interpreting GraphicsThe graphics below plot energy changes during two types of chemical reactions. Use these graphics to answer question 8.


Interpreting Graphics, continued

8. In each of these reactions, the chemical energy increases and then decreases during the course of the reaction. What does the height of the “hill” on each graph represent?

A. energy that must be added to start the reaction

B. energy released as reactant molecules approach one another

C. the potential energy of the chemical bonds in the molecules of the reactants

D. the change in total chemical energy between the reactants and the products



8. In each of these reactions, the chemical energy increases and then decreases during the course of the reaction. What does the height of the “hill” on each graph represent?

A. energy that must be added to start the reaction

B. energy released as reactant molecules approach one another

C. the potential energy of the chemical bonds in the molecules of the reactants

D. the change in total chemical energy between the reactants and the products


Interpreting Graphics, continuedIn hydrogen fuel cells, a catalyzed reaction between hydrogen and oxygen gases forms water. One of the diagrams below represents the balanced chemical equation for this reaction. Use these diagrams to answer question 9.



9. Which of the diagrams represents the balanced equation for the reaction? A. A C. C B. B D. D



9. Which of the diagrams represents the balanced equation for the reaction? A. A C. C B. B D. D

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Chemical Reactions