Question

For how many kilojoules are required to change 44.0g of ice at -12.0 degrees C to water at 85.0 degrees C?

Would this be correct:

Step 1: (2.10 J/g degrees C)(44g)(12 degrees C) = 1108.8J = 1.1088kJ

Step 2: (44g)(1mol/18g)(6.01kJ/mol)= 14.6911kJ

Step 3: (4.184J/g degreesC)(44g)(85 degreesC)= 15648.2=15.6482

1.1088+14.6911+15.6482= 31.4 kJ

For Step 1, I didn't know if the 12 degrees was supposed to be a negative.
And
For Step 3: Would it be 85 degrees or 100 degrees?

Thanks

Answer 1

<b>I didn't check the math and I don't remember all of the specific heats or heat of fusion, but the method looks ok to me.</b>

For Step 1, I didn't know if the 12 degrees was supposed to be a negative.
<b>You do this one or two ways. The first one is to reason that you are ADDING heat to raise the T from -12 to zero; therefore, it must be plus. The second way, when in doubt about reasoning, is to do it mathematically. The full equation is
mass ice x specific heat ice x (Tfinal-Tinitial). You plug alll of that stuff in and for Tfinal = 0, Tinitial is -12 and the stuff in the parentheses is [0-(-12)] which is +12 which makes the answer +.</b>
And
For Step 3: Would it be 85 degrees or 100 degrees?
<b>The problem says to 85, not to 100 (unless you want to work a different problem. :-)). </b>