Chemical Energy Flashcards
(12 cards)
What is enthalpy?
A measure of the chemical energy in a substance
What is an exothermic reaction?
What may happen in industry when working with exothermic reactions?
A reaction/process that releases heat energy
In industry exothermic reactions may require heat to be removed to prevent the temperature rising
What is an endothermic reaction?
What may happen industry when working with endothermic reactions?
A reaction/process that takes in heat energy
In industry endothermic reactions may incur costs in suppling heat energy into order to maintain reaction rate
What is the enthalpy of combustion?
The enthalpy change/amount of energy given out when one mole of a substance burns completely in oxygen
What value will the enthalpy of combustion always have?(positive or negative)
Negative value as it’s exothermic
What is the equation for calculating enthalpy change?
Eh=cm/\t
C-specific heat capacity of water(4.18kJkg-1°C-1)(stays same)
M-mass of water heated(kg)
/\t-change in temp of water
What does Hess’s law state?
That the enthalpy change for a chemical reaction is independent of the route taken(the same no matter what chemical route is taken)
What is the molar bond enthalpy?
The energy required to break one mole of bonds in a diatomic molecule
What is the mean molar bond enthalpy?
The average energy required to break one mole of bonds, for a bond that occurs in a number of compounds
Does breaking bonds require or release energy?
Will it have a positive or negative value?
It requires energy so it will have a positive value
Does making bonds require or release energy?
Will it have a positive or negative value?
It releases energy so it will have a negative value
How do you calculate the enthalpy change using bond enthalpies?
Enthalpy change=total bonds broken+(-total bonds made)
