# How would you calculate #DeltaE# of a gas for a process in which the gas absorbs 35 J of heat and does 8 J of work by expanding?

##### 1 Answer

Jul 10, 2016

This is asking you to apply the **first law of thermodynamics**:

#stackrel("otherwise known as")stackrel(DeltaU)overbrace(\mathbf(DeltaE))\mathbf( = q + w)# where:

#DeltaE# is the change in internal energy.#q# is theheat flowin the thermodynamic process.#w# is theexpansion/compression workperformed by the gas or on the gas.

Since the work is done *by the gas* (rather than *on* the gas) through the expansion,

#w = -PDeltaV = -P(V_2 - V_1)# where final volume

#V_2# isthan initial volumelarger#V_1# in an expansion, i.e. when work is negatively-signed. If work were to be positively-signed, then#V_2# would bethansmaller#V_1# .

Since the gas absorbs heat, heat flows *into* the gas, i.e.

Therefore:

#color(blue)(DeltaE) = ("35 J") + (-"8 J")#

#=# #color(blue)("27 J"#