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Many thermodynamic principles are applied to gaseous systems. When the system involves a gas, we consider "pressure-volume" (P-V) work. Many processes that we are interested in occur at a constant atmospheric pressure. The work done by (or to) a gas at constant pressure is given by equation 2. w=(-1)PAV Key Questions 6. Consider P-V work, the figure and equation 2 in the Model. If AV>0, then w0 and the gas is doing work/ is being worked on by the surroundings. If AV<0, then w0 and the gas is doing work/ is being worked on by the surroundings. (Place a "<" or a ">" in each blank and circle your answers.) 7. The relationship between a gas system's pressure (P), volume (V), number of moles of gas particles (n), and absolute temperature (7) is represented in the Ideal Gas Law (equation 3 below) and the gas constant, R. R= a. Suppose the number of moles of gas is changing (e.g., as a result of a chemical reaction) at a constant pressure and constant temperature. Complete equation 4 below. 17 _=AV RT Page 3 of 51 (4) CHEM&162 b. An automobile's engine bums octane (CsHis) as a fuel. If the fuel is in the presence of excess oxygen, it combusts "completely" according to equation 5. (At the operating temperature of the engine, all species are gaseous.) 2 CxHis(g) + 25 0:(g) → 16 CO2(g) + 18 H₂O(g) (5) i How does the number of moles of gaseous products compare with the number of moles of gaseous reactants in equation 4? A. Allg <0 B. Alls 0 C. Mg> 0 What happens to the volume of the system if the reaction shown in equation 4 occurs at constant temperature and pressure? A. AV<0 B. AV=0 C. AV>0 When the reaction of equation 4 occurs, the system does work / work is done on the system.