Thermodynamics Review Problems for Mechanical Engineering Students | Series 26

For this review problem, the very first thing to do is to express temperature in terms of pressure and volume since we aren’t provided with the temperatures at the initial and final state of hydrogen gas. This can be done, using the universal gas constant formula which is PV = mRT, as for me, I’ll be simplifying the equation like this mT = PV / R>. The reason behind that is the formula for the ΔU is expressed as a function of mass (m) and the change in temperature. And additionally, the problem has stated a keyword vessel which we can assume that the process is undertaken by the hydrogen gas is an isometric process or constant volume. Then, we can have a simplified formula for the ΔU which goes like this ΔU = cv * (ΔP*V / R). Since the units provided are in terms of English systems of units, we will be using R = 1545 / MW; wherein MW stands for molecular weight and for hydrogen gas (H2) MW is equal to 2. By using the simplified formula, we’ve found out that the change in internal energy is equal to 431 Btu. Since the problem has clearly stated that there is no heat transfer, thus Q = 0; wherein Q is heat. Finally, we can now compute for the work (W), using the formula, Q = ΔU + W. By doing so, we’ve found out that W is equal to - 431 Btu.