# How do you find q for isothermal processes?

##### 1 Answer

Jul 24, 2016

In isothermal processes, we know that by definition, **the temperature is constant**.

The internal energy *only* depends on temperature for *ideal gases*, so

#cancel(DeltaU)^(0) = q + w#

And we just get:

#color(blue)(-q = w = -PDeltaV)# where:

#q# is theheat flowin#"J"# .#w# is theexpansion/compression workin#"J"# .#DeltaV# is thechange in volumein#"L"# . Note that#"8.314472 J"/("0.083145 L"cdot"bar")# is a convenient conversion unit.#P# is a singlepressure. It tends to be in#"bar"# or#"atm"# .If

#"atm"# , you use#"8.314472 J"/("0.082057 L"cdot"atm")# for the conversion unit.