Question

How can you tell which of the two following equations to use when solving problems and why do the two different equations exist?

Why does one have moles and the other mass? How does this affect how we find internal energy for instance? I know that U= Q- W but wouldn't know which Q to use.

CynAT
  

Answer 1

Amount of heat required to increase the temprature of 1 mol by 1 kelvin.

$Q = nC_v \Delta T$

$C_V =$ Specific heat at constant Volume.

This formula is only valid when volume is constant.

U =Q -W

if volume is constant then work done will be Zero.

Then U=Q

$\Rightarrow$ Amount of heat required to increase the temprature of 1 gm by 1kelvin.

$Q= mc\Delta T$

This formula is valid for all.