Can someone check my work (Hvap/Hcond Calculation)

In summary, The student is having trouble with a problem that involves finding the heat released from cooling and heat from condensation. They use the equations q = m*deltaT*C and q = mols*Hvap to find the heat from cooling and heat from vaporization. They then add these values together to get a total of 48.221 KJ. The student also converted 1.25 mol to mass using the molar mass of methanol, which is 40 grams. They are unsure if their process is correct and ask for clarification.
  • #1
Lori

Homework Statement


I don't have an answer key to these questions and it's my first time dealing with problems like this. so was wondering if my process is correct!
upload_2017-12-12_23-51-13.png

Homework Equations


q = m*deltaT*C
q = mols*Hvap

The Attempt at a Solution


So, my reasoning behind this work is that there was heat released from cooling and also heat from condensation. So, i found heat from cooling from the equation q = mdeltaTC = 2.53 J/gC * 30g * 9.5 = 721.05 joules = 0.72105 KJ. The heat heat from vaporization is just mols*Hvap = 48.221 KJ

Added together = 48.221 KJ. Was wondering if this is correct?
 

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  • #2
Logic behind looks OK, but why 30 g?
 
  • #3
Borek said:
Logic behind looks OK, but why 30 g?
i converted the 1.25 mol to mass with MM. is this correct?
 
  • #4
And what is molar mass of methanol?
 
  • #5
Borek said:
And what is molar mass of methanol?
Gotcha. Plugged it into calculator. Should be 40 grams
 

Related to Can someone check my work (Hvap/Hcond Calculation)

1. What is the purpose of calculating Hvap/Hcond?

The purpose of calculating Hvap (heat of vaporization) and Hcond (heat of condensation) is to determine the amount of energy required to change the state of a substance from liquid to gas and vice versa. This information can be useful in various scientific and engineering applications, such as designing cooling systems or predicting the behavior of substances under different conditions.

2. How do you calculate Hvap/Hcond?

Hvap and Hcond can be calculated using the formula Q = m * ΔH, where Q is the heat energy, m is the mass of the substance, and ΔH is the enthalpy change. The enthalpy change is obtained from experimental data or calculated using other equations, such as the Clausius-Clapeyron equation.

3. What units are used for Hvap/Hcond?

The units used for Hvap and Hcond are typically joules (J) or kilojoules (kJ) per mole (mol) of the substance. However, other units such as calories (cal) or kilocalories (kcal) may also be used, especially in older literature.

4. What factors can affect the accuracy of Hvap/Hcond calculations?

The accuracy of Hvap/Hcond calculations can be affected by various factors, such as experimental errors, variations in environmental conditions (e.g. pressure, temperature), and the purity of the substance. It is important to use reliable data and perform calculations with precision to minimize errors.

5. Can Hvap/Hcond vary for the same substance?

Yes, Hvap and Hcond can vary for the same substance depending on the conditions under which the measurements are taken. For example, the heat of vaporization of water at 100°C will be different from that at 20°C due to the difference in temperature. Additionally, impurities in a substance can also affect its Hvap/Hcond values.

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