twotwntytwo
Nov1-09, 02:32 PM
This is a conceptual question...hope you guys can explain the answers that the book gives! Its frustrating me to no end. This is actually a problem in the Enthalpy chapter, calorimetry section of section exercises of the Olmsted and Williams chemistry textbook, 3rd ed.
Any help would be GREATLY appreciated! Is this just a poorly worded question, or do I have the incorrect concept?
Q: Imagine a calorimeter with a sliding piston that makes it able to perform constant pressure calorimetry experiments on a mixture of gasses and liquids
Consider burning 1.250 octane in this calorimeter, which is initially at 25 degrees celsius
Q1: Will the calorimeter temperature rise or fall?
A: Rise
[note: I understand this, since burning octane is an exothermic reaction, leading to the loss of heat from the piston to the calorimeter]
Q2: Use the ideal gas equation to determine whether the volume of the system will increase or decrease. (The temperature after burning rises about 6 degrees celcius)
A: Decrease: The volume will decrease. Although the temp rises slightly, the moles of gas decrease
[note: I don't understand this! Since it is exothermic, doesn't the reaction cause work to be performed on the piston, increasing the volume of the piston?]
Q3: Is the work, negative, positive, or zero?
A: Positive
[note: i agree with this answer. however, it seems to contradict the last answer. also, the question is not specific as to what is experiencing the work, the piston or calorimeter]
Any help would be GREATLY appreciated! Is this just a poorly worded question, or do I have the incorrect concept?
Q: Imagine a calorimeter with a sliding piston that makes it able to perform constant pressure calorimetry experiments on a mixture of gasses and liquids
Consider burning 1.250 octane in this calorimeter, which is initially at 25 degrees celsius
Q1: Will the calorimeter temperature rise or fall?
A: Rise
[note: I understand this, since burning octane is an exothermic reaction, leading to the loss of heat from the piston to the calorimeter]
Q2: Use the ideal gas equation to determine whether the volume of the system will increase or decrease. (The temperature after burning rises about 6 degrees celcius)
A: Decrease: The volume will decrease. Although the temp rises slightly, the moles of gas decrease
[note: I don't understand this! Since it is exothermic, doesn't the reaction cause work to be performed on the piston, increasing the volume of the piston?]
Q3: Is the work, negative, positive, or zero?
A: Positive
[note: i agree with this answer. however, it seems to contradict the last answer. also, the question is not specific as to what is experiencing the work, the piston or calorimeter]