Chemical Energy Flashcards
What sign is exothermic
Negative
What sign is endothermic
Positive
Definition of enthalpy of combustion
The energy when one mole of substance burns completely with oxygen
Is combustion exo or endo thermic
Exothermic - energy is released into the surroundings
What are the 3 steps to calculating enthalpy of combustion
1 - find the enthalpy - eh = cm/\T
2 - find the number of moles of fuel - not just GFM!!!
3 - find the enthalpy of combustion
What is the equation for finding the enthalpy of combustion
Enthalpy
No of moles
What is Hess’s law?
The enthalpy change for a reaction from the same reactants to the same products is equal no matter the route taken
What are the 4 steps of doing hess’s law equation
1- write out enthalpy of combustion equations ( reacting everything individually with oxygen) and add in enthalpy
2- compare equations to original ( multiply to match)
3- cancel out and combine
4- work out /\H ( kJ mol-1)
Bond breaking =
endothermic - +ve
Bond making =
Exothermic - -ve
What would happen to the equilibrium if a reactant was added
Shift right - to balance
What would happen to equilibrium if a reactant was removed
Shift left - to replace
What would happen to equilibrium if the temperature was increased
Shifts towards endothermic
What would happen to equilibrium if temperature was decreased
Shifts towards exothermic
What would happen to equilibrium if pressure was increased
Shifts towards side with the least gas molecules
