Biology Forums - Study Force

I'm trying to the final temperature for the following equation:

(10.0g)(0.129 J/gC)(Tfinal-18.0 C)+(20.0g)(0.444J/gC)(Tfinal-55.6 C)=0

(C= celsius Idk how to put the sign)

The answer is 50.83 C but when I do the calculations following the sig figs rules I get 50.85?! Are we supposed to ignore sig fig rules in calorimetry?If so, why 4 sig figs? HELP*!

This minute difference by .02 should not cause you to get an answer correct. Your answer is fine with 4 sig figs.

(10.0g)(0.129 J/gC)(Tfinal-18.0 C)+(20.0g)(0.444J/gC)(Tfinal-55.6 C)=0 <=>
1.29*(Tfinal-18.0)+ 8.88*(Tfinal-55.6)=0 <=>
1.29*Tfinal -23.22 + 8.88*Tfinal -493.728=0 <=>
10.17Tfinal = 516.948
Tfinal= 50.83C

I can't understand how you got 50.83. Maybe some calc mistake?

Shouldn't 1.29 * -18.0= -23.2? And, 8.88 *-55.6 = -494? That is what I did ;/

I figured you might did something like that. But, we usually make the rounding at the end when we get the final result. Besides, didn't you said you wanted 4 significant figures? That means, you need number with 4 figures. So, even at this point, 1.29 * -18.0= 23.22 doesn't that have 4 significant figures?

But anyways, as I said, you usually do the rounding when you find the final result (except if you encounter calculation problems, so you decide to simplify some other numbers as well)

I never said I wanted 4 significant figures o-O My professor is making me paranoid with significant figures because he applies the rules as he goes through the calculation and not at the end. But I'll follow your advice because it sounds more reasonable.