Help with enthelpy change and Hess's Law

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In summary, the conversation is discussing three separate problems involving physical processes and chemical reactions. The first problem involves the amount of ice remaining after cooling a solution of water and ice at a given temperature. The second problem involves calculating the heat of combustion and energy produced from burning a certain amount of butane. The third problem involves using data to calculate the change in enthalpy for a specific chemical reaction.
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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.
 
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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.

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FAQ: Help with enthelpy change and Hess's Law

1. What is entropy change and how is it related to Hess's Law?

Entropy change refers to the measure of disorder or randomness in a system. Hess's Law states that the overall entropy change in a chemical reaction is independent of the pathway taken, and only depends on the initial and final states of the reaction.

2. How is entropy change calculated?

Entropy change is calculated using the equation ∆S = Q/T, where ∆S is the change in entropy, Q is the heat transferred, and T is the temperature in Kelvin. Alternatively, it can also be calculated using tabulated values of standard entropies (∆S°) for each reactant and product in a reaction.

3. Why is Hess's Law important in thermodynamics?

Hess's Law is important in thermodynamics because it allows us to determine the overall change in entropy for a chemical reaction, regardless of the specific pathway taken. This is useful in understanding and predicting the behavior of chemical reactions and systems at different temperatures.

4. How can Hess's Law be applied to real-world situations?

Hess's Law can be applied to real-world situations in various ways, such as predicting the overall change in entropy in industrial processes, designing chemical reactions to minimize entropy change, and understanding the impact of temperature changes on biological systems.

5. Are there any limitations to Hess's Law?

Yes, there are limitations to Hess's Law. It assumes that the reactions involved are occurring under standard conditions and that the substances involved in the reactions are in their purest form. In reality, reactions may occur under different conditions and involve impure substances, which can affect the overall entropy change.

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