Developing Fuels - ENTHALPY + BOND ENTHALPIES Flashcards
What is the definition for Enthalpy Change of Formation?
The enthalpy change that occurs when 1 mole of a compound is formed from its elements
What are the limitations of enthalpy experiments - causing inaccurate results?
- Loss of energy to the surroundings
- loss of energy to the calorimeter
- incomplete combustion
- evaporation of fuel from the wick
Formula for percentage uncertainty is?
uncertainty of apparatus
———————————— x 100
reading of apparatus
What is enthalpy change of combustion definition?
The enthalpy change that occurs when 1 mole of substance is burned completely in oxygen.
What are the standard conditions for experiments measuring enthalpy change?
-Specified temp (25 C or 298K)
-A pressure of 1 atmosphere
-A standard concentration of 1 moldm-3
For a Hess cycle diagram regarding formation are arrows up or down?
UP
What is the definition for average bond enthalpy?
The energy needed to break one mole of bonds to give separate atoms all in the gaseous state
What is the definition of Enthalpy change of neutralisation?
Then Enthalpy change when solutions of an acid and an alkali react together under standard conditions to produce 1 mole of water
Why are calculated reaction enthalpies (using bond enthalpies) not exactly the same as experimentally calculated reaction enthalpies?
The quoted bond enthalpies are averages from all the reactions involving that bond.
(which introduces a slight error)
What type of reaction is bond breaking?
Endothermic
What type of reaction is bond making?
Exothermic
What makes a reaction Endothermic?
When more energy is taken in when BREAKING reactant bonds, than is given out making new bonds in the products
What makes a reaction Exothermic?
When more energy is given out when MAKING reactant bonds, than is given out breaking reactant bonds
What is the formula to calculate final stage of bond enthalpy calculations?
BREAKING - MAKING (values)
left - right
