6C Standard Enthalpy Change Of Combustion Flashcards
1
Q
what is standard enthalpy change of combustion
A
the enthalpy change is measured at 100KPa and a specified temperature usually 298K when 1 mole of a substance is completely burned in oxygen
2
Q
how do you find the enthalpy change of combustion of a liquid
A
- weight a spirit burner containing the liquid being tested
- add a known volume of water to a copper can
- measure the temperature of the water using a thermometer
- turn on the spirit burner
- stir the mixture constantly with a thermometer
- when the temperature was increased approximately 20 degrees from its initial temperature extinguish the flame and reweigh the burner immediately
- measure the final temperature of the water
3
Q
how do you calculate the enthalpy change of combustion
A
- calculate the heat energy, Q, transferred to the water
- calculate the number of moles of the liquid we are testing
- use the equation enthalpy change of combustion= -Q/n
4
Q
what is the equation used to find heat energy
A
Q = mass of water heated x specific heat capacity of water x temperature change of the water (Q=mcT)
5
Q
what is the specific heat capacity of water
A
4.18 J g^-1 K^-1
6
Q
what are errors in the enthalpy change of combustion of liquid experiments that could lower the actual value of it
A
- not all of the heat energy produced from burning is transferred to the water some of it is rather transferred to the surrounding
- the ethanol might have not burned completely to form carbon dioxide and water ( that means incomplete combustion therefore less energy produced and a chance of carbon soot forming at the bottom of the copper can)
- not all of the heat energy produced from burning is transferred to the water some of it is rather transferred to the copper can
- the conditions are not standard for example in combustion water vapor can form instead of liquid water
- the experiment takes a long time, so not all of the heat energy is transferred from the water to the surrounding is compensated for
