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### Difference between brackets and parentheses?

Posted: **Tue Jan 08, 2019 11:53 pm**

by **Beatrice Petelo 1F**

I noticed that when calculating K/Kc in questions 11.3 and 11.9 (6th edition), the solutions had either brackets or parentheses. Is there a difference between the two? How would I know which one to use?

### Re: Difference between brackets and parentheses?

Posted: **Wed Jan 09, 2019 9:12 am**

by **Arianna Ko 2E**

Brackets are used when referring to concentration amounts. However, once you start calculating K or Kc, although we use concentration amounts to obtain the equilibrium constant, using concentration is still an approximation. We are actually trying to find equilibrium constant using chemical activity, which has no units. So when you use concentration amounts to find K, you are assuming that the molecules are acting under ideal conditions, and use the numbers as if you are finding chemical activity, and this is when you will use parantheses with no units for the numbers inside, since again chemical activity has no units.

### Re: Difference between brackets and parentheses?

Posted: **Wed Jan 09, 2019 10:01 am**

by **Kelsey Warren 1I**

Another way to think about it is that brackets are used when you're referring to a concentration and parentheses are used when you substitute in the actual numerical value of the concentration into the K equation. For example, if one of the compounds in your chemical reaction is NH3 and its concentration is 0.30 mol/L, then in the K equation, you'd write either write [NH3] or (0.30).

### Re: Difference between brackets and parentheses?

Posted: **Wed Jan 09, 2019 10:27 am**

by **Hannah Pham 1D**

Other answers explained the reasoning, but basically you use brackets when solving for Kc and use parentheses when solving for Kp.

### Re: Difference between brackets and parentheses?

Posted: **Wed Jan 09, 2019 10:44 am**

by **JT Wechsler 2B**

Brackets are used for concentrations and will be used to calculate Kc. Parentheses are used for the partial pressures and will be used to calculate Kp.