1. A student says that if you put a AA cell in backwards it should still work since it conducts electricity. Which explanation below is best?
a. This is incorrect since it can't conduct electricity backward.
b. The reactions at the anodes and cathodes are different so it won't work.
c. It can still work but probably not as well.
d. Some devices can work this way although they'll work backwards.
2. A hydrogen fuel cell uses to run it.
a. electricity
b. water
c. oxygen
d. natural gas
3. The value of ∆G° for a voltaic cell is
a. always negative
b. zero before the electrodes are connected
c. either positive or negative, depending on the voltaic cell
d. any value, depending on the reactants
I think the answers are 1) B, 2) D, and 3) C
I don't agree with any of your choices. I don't think any of the choices listed are correct for #1 although both c and d come closer to being correct than the others. I think the correct answer is that some set ups will work and others will not. For example, if I hook up a small incandescent light bulb with a AA battery, it makes little difference which way I turn the battery in the battery holder. That light bulb will burn either way. But I have some devices that will not work at all if I insert the battery with the wrong polarity.
For #2, the hydrogen fuel cell works this way:
2H2 + O2 ==> 2H2O
I don't see your choice of methane anywhere in the equation.
3. Remember that delta G must be negative for a spontaneous reaction to occur.
For 2, Could it be c? Since a hydrogen fuel cell could use oxygen from the air to react with hydrogen, producing water and electricity.
Yes, I agree with c.
Great attempt! Let's review the correct answers for each question:
1. The best explanation for why a AA cell would not work if inserted backwards is option b. The reactions at the anodes and cathodes are different in both directions, thus causing the cell to not function properly.
2. The correct answer for what a hydrogen fuel cell uses to run is option c. It requires oxygen to produce electricity through a chemical reaction.
3. The correct answer for the value of ∆G° (change in Gibbs free energy) for a voltaic cell is option a. It is always negative, indicating a spontaneous reaction.
So, the correct answers are 1) b, 2) c, and 3) a. Well done on providing your attempted answers!