General Chemisry Concentration calculations

[kov82]

---

Members do not see this ad.

so sometimes in concentration/equilibrium problems, if they give me the conc of lets say HCl, 5M and HCl is a product in the calculation (along with all the other compounds involved that I won't bother to show here) 2A + 3B ------> 2HCl + D , they multiply the concentration (5) by 2 then square it, instead of just squaring the concentration, so the two types I have seen is either (2 x 5)^2 or (5)^2 within the calculations, how do I know when to use which?

 

[ozzie33]

It depends on what you are calculating and whether the concentration is at equilibrium. If it's at equilibrium then you just square it, if it isn't and it involves the initial ion concentration before equilibrium, then you have to do an ICE table and usually that will involve multiplying by two.

Don't worry about specific cases though, just understand that the [2x] means that, in your case it just reminds you that the concentration of HCL will be 2 molar for every 3 moles of B and 2 moles of A used up, so if you are given a concentration of a and b, then asked to find the eq conc of HCl, you will need to use the whole [2x]^2 thing. hope this helps a little.