Chapter 12, Problem 22P

A sample of benzene, C6H6, weighing 3.51 g was burned in an excess of oxygen in a bomb calorimeter. The temperature of the calorimeter rose from 25.00C to 37.18C. If the heat capacity of the calorimeter and contents was 12.05 kJ/C, what is the value of q for burning 1.00 mol of benzene at constant volume and 25.00C? The reaction is C6H6(l)+152O2(g)6CO2(g)+3H2O(l) Is q equal to U or H?

Another reaction that is used to propel rockets is N2O4(l)+2N2H4(l)3N2(g)+4H2O(g) This reaction has the advantage that neither product is toxic, so no dangerous pollution is released. When the reaction consumes 10.0 g liquid N2O4, it releases 124 kJ of heat. (a) Is the sign of the enthalpy change positive or negative? (b) What is the value of H for the chemical equation if it is understood to be written in molar quantities?

9.42 Why is enthalpy generally more useful than internal energy in the thermodynamics of real world systems?

The head of a strike anywhere match contains tetraphosphorus trisulfide, P4S3. In an experiment, a student burned this compound in an excess of oxygen and found that it evolved 3651 kJ of heat per mole of P4S3 at a constant pressure of 1 atm. She wrote the following thermochemical equation: P4S3(s)+8O2(g)P4O10(s)+3SO2(g);H=3651kJ Calculate the standard enthalpy of formation of P4S3, using this students result and the following standard enthalpies of formation: P4O10(s), 3009.9 kJ/mol; SO2(g), 296.8 kJ/mol. How does this value compare with the value given in Appendix C?

Is the following reaction the appropriate one to use in determining the enthalpy of formation of methane, CH4(g)? Why or why not? C(g)+4H(g)CH4(g)

In which of the following systems is(are) work done by the surroundings on the system? Assume pressure and temperature are constant. a. 2SO2(g)+O2(g)2SO3(g) b.CO2(s)CO2(g) c. 4NH3(g)+7O2(g)4NO2(g)+6H2O(g) d.N2O4(g)2NO2(g) e.CaCO3(s)CaCO(s)+CO2(g)

Combustion reactions involve reacting a substance with oxygen. When compounds containing carbon and hydrogen are combusted, carbon dioxide and water are the products. Using the enthalpies of combustion for C4H4 ( 2341 kJ/mol), C4H8 (2755 kJ/mol), and H2 (286 kJ/mol), calculate H for the reaction C4H4(g)+2H2(g)C4H8(g)

Dry ice is solid carbon dioxide; it vaporizes at room temperature and normal pressures to the gas. Suppose you put 21.5 g of dry ice in a vessel fitted with a piston (similar to the one in Figure 6.9 but with the weight replaced by the atmosphere), and it vaporizes completely to the gas, pushing the piston upward until its pressure and temperature equal those of the surrounding atmosphere at 24.0C and 751 mmHg. Calculate the work done by the gas in expanding against the atmosphere. Neglect the volume of the solid carbon dioxide, which is very small in comparison to the volume of the gas phase.

What is the difference between the enthalpy of reaction and the enthalpy of formation? For what chemical reaction(s) are the two quantities the same?