## Balancing equations

Novelpreet_Boparai1N
Posts: 19
Joined: Fri Jul 15, 2016 3:00 am

### Balancing equations

Do we need to memorize the charges of certain polyatomic ions for balancing redox equations?

Azeel_Mohammed_1C
Posts: 10
Joined: Wed Nov 18, 2015 3:00 am

### Re: Balancing equations

I'm pretty sure it's assumed that we should know the charges for the polyatomic ions.

Katherine_Zhuo_3B
Posts: 23
Joined: Wed Sep 21, 2016 2:57 pm

### Re: Balancing equations

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.

Jaime_Chamberlain_3G
Posts: 23
Joined: Sat Jul 09, 2016 3:00 am

### Re: Balancing equations

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?

KelseyKobayashi_2M
Posts: 21
Joined: Sat Jul 09, 2016 3:00 am

### Re: Balancing equations

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.

swatiperepa
Posts: 19
Joined: Wed Sep 21, 2016 2:59 pm

### Re: Balancing equations

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?

Emily_Vilshtein_3B
Posts: 13
Joined: Wed Sep 21, 2016 2:59 pm

### Re: Balancing equations

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.

KelseyKobayashi_2M
Posts: 21
Joined: Sat Jul 09, 2016 3:00 am

### Re: Balancing equations

Is there any way to know if the E value will end up being positive or negative before doing the calculations?

EmmaShahabi1L
Posts: 11
Joined: Wed Sep 21, 2016 2:55 pm

### Re: Balancing equations

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.

AonyaMontoya2B
Posts: 12
Joined: Fri Jun 17, 2016 11:28 am

### Re: Balancing equations

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?

samuelkharpatin2b
Posts: 55
Joined: Wed Sep 21, 2016 2:57 pm

### Re: Balancing equations

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.