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
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.
For Step 1, I didn't know if the 12 degrees was supposed to be a negative.
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 +.
And
For Step 3: Would it be 85 degrees or 100 degrees?
The problem says to 85, not to 100 (unless you want to work a different problem. :-)).
To determine the amount of energy required to change 44.0g of ice at -12.0 degrees C to water at 85.0 degrees C, you will need to consider the three steps involved in the process:
Step 1: The energy required to raise the temperature of the ice from -12.0 degrees C to 0 degrees C.
To calculate the energy required for this step, you can use the specific heat capacity of ice, which is given as 2.10 J/g°C. Since it is a temperature increase, you do not need to consider it as negative.
Energy = (specific heat capacity of ice)(mass of ice)(temperature change)
= (2.10 J/g°C)(44.0g)(12.0°C)
= 1108.8 J = 1.1088 kJ
So, your calculation for Step 1 is correct.
Step 2: The energy required to melt the ice into water.
In this step, you need to convert the mass of ice to moles using the molar mass of water (18.0 g/mol) and then multiply it by the enthalpy of fusion for water, which is approximately 6.01 kJ/mol.
Energy = (mass of ice)(1 mole / molar mass of water)(enthalpy of fusion of water)
= (44.0g)(1mol/18.0g)(6.01kJ/mol)
= 14.6911 kJ
So, your calculation for Step 2 is correct.
Step 3: The energy required to raise the temperature of water from 0 degrees C to 85.0 degrees C.
To calculate this, you can use the specific heat capacity of water, which is 4.184 J/g°C.
Energy = (specific heat capacity of water)(mass of water)(temperature change)
= (4.184 J/g°C)(44.0g)(85.0°C)
= 15648.2 J = 15.6482 kJ
So, your calculation for Step 3 is correct.
Adding up the energies from all three steps:
Total energy = Step 1 energy + Step 2 energy + Step 3 energy
= 1.1088 kJ + 14.6911 kJ + 15.6482 kJ
= 31.4481 kJ
Therefore, the correct amount of energy required to change 44.0g of ice at -12.0 degrees C to water at 85.0 degrees C is approximately 31.4 kJ.