Joule Units? TBR phyics Ch.3

[Thoroughbred_Med]

"20. If a 10.0 g heating coil goes from 20 degrees C to 40 degrees C in 3.00 seconds, then what was the average power supply during this time if Ccoil = 3.00 J/g*K"

A. 0.20 W
B. 20 W
C. 200 W
D. 1800 W


I know that P = W/t and that the units are Watts = J/s but TBR says the answer is 200 W. To me, it looks like they never converted g to kg .... and Joule = kg*s^2/m^2

the math is Q = mcdeltaT which equals work and you just divide that by time to get power. When I do the math I get (.6J/3.0 seconds) = 0.2 W

what am I missing? Thanks!

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[5words]

What you're missing is that the units for mass are different for Physics and Chem. In Physics, the mass is expressed in KG whereas in Chem the mass is expressed in g. Because this question pertains to GCHem, the units ought to be grams and not Kg.

 

[aldol16]

Always use dimensional analysis. Units will be your friend on this exam. The specific heat capacity is given in J/g*K, so keep everything in those units so that they cancel.