Knowledge Base Article
Article ID: 27304 [Last Updated8/30/2002 10:26:41 AM]
Summary:
Why do you round to 6 x 10^2 cal/gC in Module #2, practice problem 10, Exploring Creation with Chemistry?
Article:
I rounded it to 6x10^2 because of significant figure rules. The Delta_T for the water and calorimeter is determined by subtracting 24.2 from 25.1:
Delta_t = 25.1 C - 24.2 C
According to Module #1 (pp. 25-26), the rules for addition and subtraction are DIFFERENT than those of multiplication and division. In addition and subtraction, you look at precision (decimal place), NOT number of significant figures. In this problem, both numbers go out to the tenths place, so my answer can only go out to the tenths place. Thus, the answer is 0.9 C.
When I plug that into the equation for c, I am now multiplying and dividing. When multiplying and dividing, you COUNT SIGNIFICANT FIGURES. Since 0.9 C has only 1 significant figure, my answer can have only 1 significant figure. Thus, the answer is 600 cal/gC, or 6 x 10^2 cal/gC.