Agas mixture at 490.0°c and 127 kpa absolute enters a heat exchanger at a rate of 60.0 m3/hr. the gas leaves the heat exchanger at 170.0°c. the change in enthalpy of the gas during the cooling process is -4.70 kj/mol. what is the heat required in kw? assume the gas behaves ideally and that the changes in kinetic and potential energy are negligible.

Explanation:

According to the ideal gas equation, PV = nRT.

or,            n =

As it is given that pressure is 127 kPa or 127000 Pa (as 1 kPa = 1000 Pa), volume is 60.0 , R is gas constant equals 8.314 J/K/mol, and temperature is (490 + 273) K = 763 K.

Hence, putting these values into the above equation as follows.

                    n =

                        =

                        = 0.320 mol/s

Therefore, heat required will be calculated as follows.

  change in enthalpy of the gas during the cooling process × mole flow

                      = 4.70 kJ/mol × 0.320 mol/s

                     = 1.50 kW

Thus, we can conclude that heat required in kW for the given situation will be 1.50 kW.

1. the question asks the most appropriate, which seems to rule out "all of the above." your choice appears to be the correct one.

2. the protocol described is good for identifying correlation, but not cause and effect. for cause/effect, you need to devise a protocol that will assign the treatment (or not) to groups that have essentially the same "demographics" with respect to all the other variables. your choice regarding control group seems appropriate. random assignment of treatment (choice d) may be appropriate also. (i think you can argue that b and d are just different descriptions of the same method.)

3. d will randomize the birds, but may not guarantee there are 10 in each group. e will do both, so seems the better choice.

comment on question 2

based on the problem statement, it seems clear that confident, attentive drivers are more likely to use daytime running lights. so, the protocol might need to be devised in such a way that the lights would be turned on or off without the driver's knowledge. (an attentive driver will figure it out.) assigning a confident, attentive driver to a group required to drive without running lights might mess with his/her confidence and attentiveness. you don't want your experiment to do that. (nor do you want the experiment to subject a driver to greater risk of accident as a consequence of driving without running lights.) experiments involving human safety are always problematic.

i believe the answer is a.