5% rule

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Jorja De Jesus 2C
Posts: 121
Joined: Sat Jul 20, 2019 12:15 am

5% rule

Postby Jorja De Jesus 2C » Sat Jan 18, 2020 11:52 pm

What is the 5% rule and how do you apply it?

Alexandra Bartolome 2H
Posts: 102
Joined: Sat Jul 20, 2019 12:17 am

Re: 5% rule

Postby Alexandra Bartolome 2H » Sun Jan 19, 2020 12:43 am

When calculating the percent ionization and it is less than 5%, it confirms that the approximation of x in the ICE table is okay and the use of the quadratic formula is not necessary.

805097738
Posts: 180
Joined: Wed Sep 18, 2019 12:20 am

Re: 5% rule

Postby 805097738 » Sun Jan 19, 2020 12:18 pm

because the change in x is so small, the original molarity of the molecule being changed by x is a suffice approximation.

Robert Tran 1B
Posts: 118
Joined: Thu Jul 11, 2019 12:15 am

Re: 5% rule

Postby Robert Tran 1B » Sun Jan 19, 2020 12:50 pm

If the percent deprotonation is less that 5%, then when we calculate equilibrium concentrations, we can ignore the x values relative to the initial concentration because it is not significant.

Andres Merlos 2L
Posts: 46
Joined: Wed Sep 18, 2019 12:17 am

Re: 5% rule

Postby Andres Merlos 2L » Sun Jan 19, 2020 1:00 pm

The 5% rule generally applies to approximation when trying to find x, after performing an ICE table. Instead of using the quadratic formula, you can disregard x relative to the initial if what you get from the approximation is less than 5% of the initial value. The procedure to finding that value is through the percent Ionization.

Matt F
Posts: 100
Joined: Sat Aug 17, 2019 12:17 am

Re: 5% rule

Postby Matt F » Sun Jan 19, 2020 3:33 pm

The 5% rule can be applied after making an approximation for x. You calculate x/[initial concentration given] and if the value is less than 5% (0.05) then the approximation is valid. However, if the value is greater than 5% then you must reject the approximation and recalculate x

Cavalli_1H
Posts: 92
Joined: Thu Sep 19, 2019 12:15 am

Re: 5% rule

Postby Cavalli_1H » Sun Jan 19, 2020 4:00 pm

it means you can only approximate a value for x on an ice table. you can sidestep the quadratic equation when you apply the approximation threshold. you do this because the value is so insignificant that it doesn't necessarily affect the solution

Ritu Gaikwad 2E
Posts: 52
Joined: Thu Jul 11, 2019 12:16 am

Re: 5% rule

Postby Ritu Gaikwad 2E » Sun Jan 19, 2020 4:32 pm

The 5% rule is used normally in indicating if when setting up the Kc expression if x should be factored into the concentration of the initial reactant. You normally approximate without using that x and if the resulting value x/(initial conc) is less than 5% it is valid to not factor that x in the concentration of the initial reactant.

kevinolvera1j
Posts: 103
Joined: Fri Aug 02, 2019 12:15 am

Re: 5% rule

Postby kevinolvera1j » Sun Jan 19, 2020 7:07 pm

The 5% rule is sort of like checking your work. If you approximated by ignoring x, if the percent ionization was less than 5%, then the approximation was fine.

Charysa Santos 4G
Posts: 107
Joined: Wed Sep 18, 2019 12:21 am

Re: 5% rule

Postby Charysa Santos 4G » Sun Jan 19, 2020 7:09 pm

The 5% rule is for checking whether or not your approximation is valid. This is usually if the K is less than 10^-3 and you take out the X from the denominator of your equilibrium expression.

Trent Yamamoto 2J
Posts: 111
Joined: Sat Aug 17, 2019 12:18 am

Re: 5% rule

Postby Trent Yamamoto 2J » Sun Jan 19, 2020 9:29 pm

The 5% Rule essentially means you can approximate the value for x on an ice table because the value is so small it doesn't make a significant change in the concentration. For example, Professor Lavelle talked about how a millionaire giving away $1,000 would barely notice the difference.


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