1. Questions

LAB!!

I have to find the molar enthalpy of combustion of pentane. I have this info:

5C(s) + 6H2 >>> C5H12 Hf= -173.5kJ
C+O2>>> CO2 Hf= -393.5kJ
H2 + 1/2O2 >>> H2O Hf= -241.8kJ
H2O >>> H2O Hf= +44.0kJ

THEN I am given this:
mass of pentane= 2.15g
volume of water equivalent to calorimeter= 1.24L
initial temp. of calorimeter & contents= 18.4 degrees celcius
final temp. of calorimeter & contents= 37.6 degrees celcius

The one thing I don't get is why the give me the equations with the Hf. I don't get it. As well, what am I supposed to do with the rest of the information? Can you please help me get started. Thanks*


The equations, I think, are there to allow you to calculate, from the values given, the heat of combustion that you SHOULD get from experimental data. Reverse equation 1, then add equation 2 (multiplied by 5) and add equation 3 (multiplied by 6). You left something off the last equation but I assume it is H2O liquid ==> H2O steam (or it may be the other way around). You will need to add or subtract that 44 kJ (remember that is per mole and you have 6 mols H2O ) as appropriate. Also, remember that if you multiply an equation by 5 or 6 to also multiply the kJ and if you reverse the equation you must reverse the sign given. Finally, the last part is an experimental part.
Delta H = mass x specific heat water x (Tf - Ti) where Tf is the final temperature and Ti is the initial temperature. I would assume the density of water to be 1.00 g/L here so the mass of H2O would be 1,240 g. The specific heat of water is 4.18 J/g*C. This should give you the experimental value for the combustion of pentane FOR 2.15 GRAMS. You want the value per mol. I hope this helps.

  1. 👍
  2. 👎
  3. 👁
Hey!

  1. i need help

    1. 👍
    2. 👎
    jemima

Respond to this Question

First Name

Your Response

Similar Questions

  1. chemistry

    The complete combustion of ethanol, C2H5OH (FW = 46.0 g/mol), proceeds as follows: C2H5OH(l) + 3 O2(g) → 2 CO2(g) + 3 H2O(l) ΔH = −555 kJ What is the enthalpy change for combustion of 15.0 g of ethanol

  2. Chemistry

    Can someone answer this question? The enthalpy of combustion of solid carbon to form carbon dioxide is -393.7 kJ/mol carbon, and the enthalpy of combustion of carbon monoxide to form carbon dioxide is -283.3 kj/mol CO. Use these

  3. Chemistry

    Two liquids, n-pentane and 1-butanol, have nearly the same molecular weight, but significantly different temperature values. Why is there a difference between these two substances, based on their intermolecular forces? temperature

  4. chemistry

    The molar enthalpy of vaporization for water is 40.79 kJ/mol. Express this enthalpy of vaporization in joules per gram. b. The molar enthalpy of fusion for water is 6.009 kJ/mol. Express this enthalpy of fusion in joules per gram.

  1. Chemistry

    If the standard enthalpy of combustion of octane, C8H18(l) is -5471 kJ/mol, calculate the enthalpy change when 1.00 kg of octane are burned. the molar mass of octane is 114 g/mol

  2. chemistry

    Calculate enthalpy change of reaction for the combustion of gaseous ethanol. C2H5OH + 3O2 >> CO2 + 3H2O. Using standard molar enthalpies of formation. C2H5OH -235.3 ( it's negative sign) CO2 -393.5 H2O -241.8 (1) Calculate the

  3. chemistry

    2.9 The standard enthalpy of formation of the metallocene bis(benzene)chromium was measured in a calorimeter. It was found for the reaction Cr(C6H6)2(s) → Cr(s) + 2 C6H6(g) that . Find the corresponding reaction enthalpy and

  4. Chemistry

    C2H5OH(l) + 3 O2(g) -> 2 CO2(g) + 3 H2O(g) During an experiment 10.00 g of ethanol is completely burned in air to release CO2(g) and H2O(g) as shown in the equation above. During the combustion, 296.6 kJ of heat energy is

  1. chemistry

    The change in internal energy for the combustion of 1.0 mol of octane at a pressure of 1.0 atm is 5084.3kJ. if the change is enthalpy is 5074.1kJ, how much work is done during the combustion?

  2. chemistry BOB

    is this the answer to B ) CH3CH2OH + 3O2 → 2CO2 + 3H2O In winemaking, the sugars in grapes undergo fermentation by yeast to yield CH3CH2OH and CO2. During cellular respiration, sugar and ethanol are "burned" to water vapor

  3. Chemistry

    The enthalpy of combustion of benzoic acid is –26.4 kJ/g. What is the enthalpy of combustion expressed in joules per kilogram?

  4. Chemistry

    If the theoretical molar enthalpy of solution for NH4Cl(aq) is +14.7 KJ/mol, what mass of NH4Cl is needed to decrease the temperature of 100.0g of water by -20.0oC. Write a thermochemical equation for this process, including the

You can view more similar questions or ask a new question.