Enthelpy Change of Combustion.

This will give you a value of -20900J. Then, when you calculate the moles of ethanol, you should be dividing by its molar mass (46g/mol), not its mass in grams. This will give you a value of -454kJ/mol, which is closer to the given answer of -1.37 x 10^3 kJ/mol.
  • #1
jinhuit95
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Homework Statement


When 1.00g of ethanol was burned under a container of water, it was found that 100g of water was heated from, 15°C to 65°C, The process was known to be only 70% efficient. Calculate the enthalpy change of combustion of ethanol taking specific heat capacity of water to be 4.18 J g^-1 k^-1.


Homework Equations


q= mc ΔT; ΔHr= - q/ moles of limiting reagent.


The Attempt at a Solution


I calculate q = 100 x 4.18 x 50 x(70/100) = 14630J.
Then I found the number of moles of ethanol which is 1/46 = 0.0217
Therefore enthalpy change will then be -14630/0.0217 = -672980J = -673 kJ mol^-1 but the answer given is -1.37 x 10^3 kJ mol^-1. Where did I go wrong??
 
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  • #2
In your first step you should be dividing by 70% rather than multiplying by 70%.
 

FAQ: Enthelpy Change of Combustion.

1. What is enthalpy change of combustion?

Enthalpy change of combustion is a measure of the amount of heat released when a substance is completely burned in oxygen. It is also known as the heat of combustion.

2. How is enthalpy change of combustion calculated?

The enthalpy change of combustion is calculated by subtracting the enthalpy of the products from the enthalpy of the reactants. This gives the amount of heat released during the combustion reaction.

3. What factors affect the enthalpy change of combustion?

The enthalpy change of combustion is affected by the type of fuel being burned, the amount of oxygen present, and the temperature and pressure of the reaction environment. Other factors such as the efficiency of the combustion process and the presence of impurities in the fuel can also affect the enthalpy change.

4. Why is enthalpy change of combustion important?

The enthalpy change of combustion is important because it allows us to calculate the amount of energy that can be obtained from a fuel. This is useful in many industrial and technological applications, such as designing efficient engines and determining the potential energy output of different fuels.

5. How can enthalpy change of combustion be measured?

Enthalpy change of combustion can be measured using a bomb calorimeter, which is a device that allows for the complete combustion of a substance in a controlled environment. The temperature change of the surrounding water is then measured and used to calculate the enthalpy change of the combustion reaction.

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