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 the heat flow in the thermodynamic process.w is the expansion/compression work performed 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 is larger than initial volumeV_1 in an expansion, i.e. when work is negatively-signed. If work were to be positively-signed, thenV_2 would be smaller thanV_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"