If equal masses of o2 and hbr are in separate

General Chemistry I

Exam 3

Due date: April 4, 2020, at 5:00 pm

Name:

1. Copper metal has a specific heat of 0.385 J/g·C. Calculate the amount of heat required to raise the temperature of 22.8 g of Cu from 20.0C to 875C.

2. How many degrees of temperature rise will occur when a 25.0 g block of aluminum absorbs 10.0 kJ of heat? The specific heat of Al is 0.900 J/g·C.

3. A glass containing 200. g of H2O at 20C was placed in a refrigerator. The water loses 11.7 kJ as it cools to a constant temperature. What is its new temperature? The specific heat of water is 4.184 J/g·C.

4. When 0.7521 g of benzoic acid was burned in a calorimeter containing 1,000. g of water, a temperature rise of 3.60C was observed. What is the heat capacity of the bomb calorimeter, excluding the water? The heat of combustion of benzoic acid is -26.42 kJ/g.

5. Which of these processes is endothermic?

A. O2(g) + 2H2(g) 2H2O(g)

B. H2O(g) H2O(l)

C. 3O2(g) + 2CH3OH(g) 2CO2(g) + 2H2O(g)

D. H2O(s) H2O(l)

6. 0.1326 g sample of magnesium was burned in an oxygen bomb calorimeter. The total heat capacity of the calorimeter plus water was 5,760 J/C. If the temperature rise of the calorimeter with water was 0.570C, calculate the enthalpy of combustion of a mol of magnesium. Mg(s) + 1/2O2(g) MgO(s)

7. Ethanol undergoes combustion in oxygen to produce carbon dioxide gas and liquid water. The standard heat of combustion of ethanol, C2H5OH(l), is -1366.8 kJ/mol. Given that [CO2(g)] = -393.5 kJ/mol and [H2O(l)] = -285.8 kJ/mol, what is the standard enthalpy of formation of ethanol?

8. Glycine, C2H5O2N, is important for biological energy. The combustion reaction of glycine is given by the equation: 4C2H5O2N(s) + 9O2(g) 8CO2(g) + 10H2O(l) + 2N2(g) = -38 =57 kJ. Given that [CO2(g)] = -393.5 kJ/mol and [H2O(l)] = -285.8 kJ/mol, calculate the enthalpy of formation of glycine.

9. Calculate the standard enthalpy of formation of liquid methanol, CH3OH(l), using the following information: C(graph) + O2 CO2(g) H = -393.5 kJ/mol H2(g) + (1/2)O2 H2O(l) H = -285.8 kJ/mol CH3OH(l) + (3/2)O2(g) CO2(g) + 2H2O(l) H = -726.4 kJ/mol

10. Calculate the standard enthalpy change for the reaction 2C8H18(l) + 21O2(g) 8CO(g) + 8CO2(g) + 18H2O(l).

11. A sample of nitrogen gas has a volume of 32.4 L at 20C. The gas is heated to 220ºC at constant pressure. What is the final volume of nitrogen?

12. A sample of N2 gas occupies 2.40 L at 20C. If the gas is in a container that can contract or expand at constant pressure, at what temperature will the N2 occupy 4.80 L?

13. If the pressure of a gas sample is quadrupled and the absolute temperature is doubled, by what factor does the volume of the sample change?

14. The temperature of an ideal gas in a 5.00 L container originally at 1 atm pressure and 25C is lowered to 220 K. Calculate the new pressure of the gas.

15. Calculate the volume occupied by 35.2 g of methane gas (CH4) at 25C and 1.0 atm. R = 0.0821 L atm/Kmol.

16. Calculate the number of kilograms of helium needed to inflate a balloon to a volume of 100,000 L at an atmospheric pressure of 250 mmHg and a temperature of -35C.

17. Calculate the density, in g/L, of chlorine (Cl2) gas at STP.

18. A 0.271 g sample of an unknown vapor occupies 294 mL at 140C and 847 mmHg. The empirical formula of the compound is CH2. What is the molecular formula of the compound?

19. Chlorine gas can be prepared in the laboratory by the reaction of solid manganese dioxide with hydrochloric acid. (The other reaction products are aqueous manganese chloride and water.) How much MnO2 should be added to excess HCl to obtain 275 mL of chlorine gas at 5.0C and 650 mmHg?

20. If equal masses of O2(g) and HBr(g) are in separate containers of equal volume and temperature, which one of the following statements is true?

A. The pressure in the O2 container is greater than that in the HBr container.

B. There are more HBr molecules than O2 molecules.

C. The average velocity of the O2 molecules is less than that of the HBr molecules.

D. The average kinetic energy of HBr molecules is greater than that of O2 molecules.

E. The pressures of both gases are the same.