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### Balancing equations

Posted: Sun Feb 12, 2017 4:34 pm
Do we need to memorize the charges of certain polyatomic ions for balancing redox equations?

### Re: Balancing equations

Posted: Sun Feb 12, 2017 9:05 pm
I'm pretty sure it's assumed that we should know the charges for the polyatomic ions.

### Re: Balancing equations

Posted: Tue Feb 14, 2017 9:23 am
General polyatomic ions such as NO3-, SO42-, will need to be known, as well as common charges such as O2-, H1+, and 1+ charges for alkali metals.

### Re: Balancing equations

Posted: Tue Feb 14, 2017 4:41 pm
When we are given the Voltage number but we are balancing the equations, does the number change as the equation is multiplied by a constant or a negative?

### Re: Balancing equations

Posted: Tue Feb 14, 2017 7:24 pm
Since Eo is an intensive property, it is fixed. I believe the only time it changes sign is when you are writing out the half reactions and need to flip signs so that one is reduced and the other is oxidized.

### Re: Balancing equations

Posted: Wed Feb 15, 2017 1:29 pm
I keep getting confused on when you need to switch the sign of the reduction potential. If the given half equation has already flipped the reduction potential so that it is negative, do you simply add together the reduction potentials or do you flip the reduction potential back, and then do cathode - anode?

### Re: Balancing equations

Posted: Wed Feb 15, 2017 3:30 pm
swatiperepa wrote:I keep getting confused on when you need to switch the sign of the reduction potential. If the given half equation has already flipped the reduction potential so that it is negative, do you simply add together the reduction potentials or do you flip the reduction potential back, and then do cathode - anode?

If you are combining two half reactions, you only flip the sign of the reduction potential of the half-reaction that is being used as the oxidation part. Then you would add the reduction potentials like you would when using the Hess method of adding reactions. Just make sure that you do not multiply by any constants. This answer should be equivalent to using the reduction potential equation by subtracting cathode minus anode except in this case you leave all the reduction potentials as given. Do not flip any signs if you choose to use the equation instead of adding reactions like the Hess method.

### Re: Balancing equations

Posted: Wed Feb 15, 2017 3:44 pm
Is there any way to know if the E value will end up being positive or negative before doing the calculations?

### Re: Balancing equations

Posted: Wed Feb 15, 2017 10:20 pm
If you're trying to estimate whether or not the reaction will be positive at the beginning, pay close attention to the initial E value of the cathode. Since the equation for the charge of a cell is cathode - anode if the cathode is a very high positive number, it's likely the total cell charge will be positive.

### Re: Balancing equations

Posted: Tue Feb 21, 2017 8:31 pm
When you balance equations what are like some "steps" that could be applied? and how do you know when and what side of the reaction to put H2O or OH and O2 and H?

### Re: Balancing equations

Posted: Wed Feb 22, 2017 6:31 pm
I would say that knowing the general polyatomic ion charges would be a good thing, but you definitely should know the charges of ions based on their group/family in the periodic table.