AP Chemistry : Thermochemistry and Kinetics

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

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Example Question #3 : Galvanic (Voltai) And Elecrolytic Cells

What is true about the current flow in a galvanic cell?

Possible Answers:

It travels from anode to cathode

It flows in the direction of electron flow

It travels from cathode to anode

Galvanic cells do not have a current

Correct answer:

It travels from cathode to anode

Explanation:

In a galvanic cell, the electrons will flow from the anode to the cathode; however, current travels in the opposite direction of the electrons by convention. In chemical cells, current is defined by the direction in which protons would flow. As a result, current flows from the cathode to the anode.

Keep in mind that reduction occurs at the cathode and oxidation occurs at the anode. Electrons are thus constantly moving from the anode to the cathode. Since the current will be opposite to the flow of electrons, we can conclude that it must flow from cathode to anode.

Example Question #4 : Galvanic (Voltai) And Elecrolytic Cells

The following galvanic cell is created:

      

Which of the following takes place at the cathode?

Possible Answers:

Copper loses electrons

Gold ions receive electrons

Copper gains electrons

Gold loses electrons

Correct answer:

Gold ions receive electrons

Explanation:

Reduction always takes place at the cathode. This means that a substance is receiving electrons.

In the reaction, the gold ions are receiving electrons in order to create gold atoms. This takes place at the cathode.

Copper ions and gold are products, and will not be oxidized or reduced. Copper is reduced at the anode during this reaction.

Example Question #1 : Cell Potential And Free Energy

1.  

2.  

3. 

What is ? Is reaction 3 spontaneous?

Possible Answers:

, spontaneous

, spontaneous

, nonspontaneous

, nonspontaneous

Correct answer:

, nonspontaneous

Explanation:

There are two concepts to consider in this problem.  First, the question asks for the .  Reaction 3 has  being reduced so the potential for the half reaction becomes negative.  half reaction appears the same in reaction 3 so the potential is the same. Second, negative voltages indicate non-spontaneity and positive voltages are spontaneous.  

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