Chemistry assignment
CHM 101 Module Four Additional Homework Problems
1. In order to verify the heat of reaction, a chemist mixes 1 liter of 1 M NaOH and 1 liter of 1 M HCl. The initial temperature of the two solutions is 25C. The specific heat of water is 4.184 J/gC.
The enthalpy of reaction of the following is –58 kJ/mol.
HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)
a) Is this reaction exothermic or endothermic? (Will the temperature increase or decrease?)
2. The same reaction takes place in two different vessels, which are initially at atmospheric pressure (1 atm). The first vessel is rigid and does not expand with change in pressure; the second vessel will expand to maintain a pressure of 1 atm inside. Over the course of a reaction, the second vessel expands by 1 liter.
a) What is the amount of PV work done by the reaction for each of the vessels?
b) Which vessel’s content has a higher enthalpy?
c) Based on the answer to part b, which vessel would you expect to have a higher temperature?
3. Use the enthalpies of formation in the table below to answer the following questions.
|
Substance |
Enthalpy of Formation (kJ/mol), 298 K |
|
Oxygen (O2)(g) |
0 |
|
Methane (CH4)(g) |
-74.8 |
|
Carbon Dioxide (CO2)(g) |
-393.5 |
|
Water (H2O)(g) |
-241.8 |
|
Water (H2O)(l) |
-285.8 |
a) Calculate the change in enthalpy for the combustion of methane using the values in the table above (assuming that the system remains at 298 K) for the combustion of methane to form carbon dioxide and gaseous water.
b) Repeat this calculation assuming that the product is liquid water.
c) Explain what this difference represents.