Page 1 of 1

SB C/P Q4 and 8

Posted: Sun Aug 11, 2019 7:50 pm
by Amber9
Q5 what equation do you use?

Q8 the passage states "ΔHu is the difference between the laser pulse energy Em and the heat detected ΔHnr"
Why is the answer 0 I thought dissociation has to do with enthalpy


Re: SB C/P Q4 and 8

Posted: Mon Aug 12, 2019 12:53 pm
by NS_Tutor_Mathias
Just the definition of power, or what we can call the power-energy relationship: Power = E/t =W/t

Power is the rate at which you are doing work. Therefore, Power * time = energy.

Try out both lasers and see what pops out!

This is possibly my all-time favorite from the section bank for reasoning about experimental design. It requires us to realize that the energy meter is not how photoacoustic calorimetry determines bond dissociation enthalpy at all: It is just a device to make sure that if our microphone picks up a signal, all the energy sent to the sample was actually absorbed. If it was not, the energy meter will detect some non-0 value (to within 3.4 eV of error) - and this will suggest in turn that we used an inappropriate pulsed laser.