## what equation to use for q

$\Delta U=q+w$

Shelbyhamilton 3H
Posts: 37
Joined: Fri Sep 26, 2014 2:02 pm

### what equation to use for q

how do we know when to use
q=nc delta t
or
q= mc delta t

basically when do we have to use moles or grams and is there a way to easily distinguish between the two?!

thank you SO much for your help its greatly appreciated

Niharika Reddy 1D
Posts: 127
Joined: Fri Sep 26, 2014 2:02 pm

### Re: what equation to use for q

It depends on the type of heat capacity you are using. If it's specific heat capacity and the units are in J/g°C or J/g•K, use grams and your second equation. If it's molar heat capacity and the units are J/mol°C or J/mol•K, use moles and your first equation.

Our objective is to find heat in J, so we need to do whatever it takes to cancel out the other units. For example, when using specific heat capacity, multiplying by the change in temperature cancels out the °C or K unit depending on which you choose to use, and multiplying by mass in grams cancels out the unit "g" from the specific heat term, leaving just joules.

Justin Le 2I
Posts: 142
Joined: Fri Sep 26, 2014 2:02 pm

### Re: what equation to use for q

You might also see an equation that looks like q=CdeltaT. A capital C means heat capacity, and the two that are listed in the first post are just different types of heat capacity.