Help with enthalpy change and Hess's Law

  • #1

Homework Statement


- 82 grams of ice is added to 0.15 liters of water at 35 degrees C. If the solution is allowed to cool to 0 degrees C, how much ice remain? (Heat of fusion of ice is 333 J/g)

- Many cigarette lighters contain liquid butane, C4H10 for which ΔH(formation) = -127 kJ/mol. Calculate the heat of combustion of this reaction, and then how much energy is produced when 1.00 grams of liquid butane is burned. The products of the combustion are CO2 and water vapor.

- Using the following data:

Ca + 2C = CaC2 H°=-62.8 kJ
Ca + 1/2O2 = CaO H°= -635.5 kJ
CaO + H2O = Ca(OH)2 H°= -653.1 kJ
C2H2 + 5/2O2 = 2CO2 + H2O H°= -1300 kJ
C + O2 = CO2 H°= -393.5 kJ

Calculate the change in enthalpy for the following equation

CaC2 + 2H2O = Ca(OH)2 + C2H2



Homework Equations



mc=ΔT
q=mcΔT

The Attempt at a Solution



I know that for the Hess Law problem, I need to cancel out unimportant elements and compounds, but I'm completely lost with the other two problems.
 

Answers and Replies

  • #2
188
12
Welcome to PF.

According to the forum policy, you need to show your solution for the problem.

We don't cancel out "unimportant" stuff, we just add chemical equations and some compounds cancel each other out in the process.

For the first problem, how is heat related to the cooling of 0.15 liters of water from 35 degrees C to 0?

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Now, do TRY to solve all problems. Post your steps here. Think twice and don't be afraid to make mistakes.

mafagafo
 

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