Fuels Flashcards
Is the enthalpy change for an exothermic reaction positive or negative?
Exothermic reactions have a negative enthalpy change
Is the enthalpy change for an endothermic reaction positive or negative?
Endothermic reactions have a positive enthalpy change
If the total energy of the products is less than that of the reactants is the reaction exothermic or endothermic?
Exothermic
If the total energy of the products is more than the reactants is the reaction exothermic or endothermic?
Endothermic
What are calorimeters used to measure?
Energy of reaction, the amount of heat involved in a chemical reaction.
What is the equation for the calibration factor of a calorimeter?
CF = n x Hc / ∆T
or
CF = E / ∆T
or
CF = VIt / ∆T
How do we account for heat loss to the environment when calculating the temperature change to find CF?
By taking recordings of the temperature at regular intervals, the data can be graphed over time and the actual temperature change can be seen in and compared with the final temperature after the mixture was left to cool
What units are energy from food in?
kJ /g
What are some assumptions made when calculating energy released from food?
The heat of combustion of food assumes we are burning the nutrient in an environment containing excess oxygen. In reality, during digestion the energy value can be less than expected.
What is likely to be the difference between the energy released by a food during an experiment where it was burnt, and when the energy released into your body following digestion?
The energy will measure slightly higher during the experiment than during cellular respiration.
What is the process of producing biodiesel?
A transesterification reaction between plant/animal triglycerides and alcohol creates biodiesel (a mixture of methyl esters) and also glycerol
What is the molecular formula of glycerol?
C3H8O3
What is the structure and molar mass of a methyl ester?
CH3 - O - (C=O) - R
The molar mass of a methyl ester is 59 + 12C + H + 1
If a fatty acid used to create a triglyceride that will be used to create biodiesel has a total of 16 carbons (palmitoleic acid) then how many total carbons will be in the biodiesel molecule?
- As the carbon chain length will be the same as that of the fatty acid, but one more carbon is on the “methyl” side of the ester functional group.
What catalyst is required in the transesterification of biodiesel?
NaOH or KOH