Chem B: Unit 4

Two substances are dissolved in water and start to react. Which statement accurately describes the appearance of the solution when it reaches equilibrium?

No changes will be apparent, as the forward and reverse reactions continue.

Use the equation showing the dissociation of iron thiocyanate in water to answer the question. FeSCN2+(aq) ⇄ Fe3+(aq) + SCN-(aq) In solution, FeSCN2+ ions are red, Fe3+ ions are pale yellow, and SCN- ions are colorless. Given that iron ions bind with hydroxide ions to produce solid Fe(OH)3, which statement about the solution is correct?

Decreasing the pH will release Fe3+ ions and cause the solution to become more red.

Use the reaction to answer the question. 3MnO42-(aq) + 4H+(aq) ⇄ 2MnO4-(aq) + 2H2O(l) + MnO2(s) In this reaction, MnO42- ions are green and MnO4- ions are purple. Which substance, when added to the solution, would make the solution more purple?

MnO42- ions

Which statement explains what it means for a chemical reaction to be at equilibrium?

The rate of the forward and backward reactions are equal.

How can you tell that this process is not at equilibrium?

The reaction mixture is not complete as reactants are still being added to the system.

Why is it not useful to talk about equilibrium in the context of baking?

The reactions that happen in baking are not reversible reactions

Which statement best explains what would happen if a reactant were added to a system in equilibrium?

The system would shift toward the products to oppose the change.

Use the equation showing the dissociation of iron thiocyanate in water to answer the question. FeSCN2+(aq) ⇄ Fe3+(aq) + SCN-(aq) In solution, FeSCN2+ ions are red, Fe3+ ions are pale yellow, and SCN- ions are colorless. When a solution at equilibrium is orange, which change would cause the solution to become pale yellow?

adding an ion that causes SCN- to precipitate

Use the reaction to answer the question. Cr2O72-(aq) + H2O(l) ⇄ 2CrO42-(aq)+ 2H+(aq) Given Cr2O72- ions are orange and CrO42- ions are yellow, which change to the reaction would most effectively make the solution more orange?

decreasing the pH

Use the description of a process to answer the question. A person eats a candy bar. The person's blood sugar rises. The body produces insulin to reduce the person's blood sugar. The person's blood sugar drops. The person returns to a healthy level of blood sugar and remains there. In which step of the process is the person most likely at chemical equilibrium?

in step 5 when the person returns to a healthy level of blood sugar and remains there