Energetics Flashcards
What is an exothermic reaction
A reaction in which produces heat
-eg combustion, respiration or neutralisation
What is an endothermic reaction
Reaction that absorbs/requires heat to occur
-E.g. evaporation (heat the water) ice cube melting, heat is absorbed while melt
What is energy measured in
Kj
Is bond breaking is exothermic or endothermic
It’s endothermic because to break bonds you have to put energy in which is endothermic
Is making bonds exothermic or endothermic
It’s exothermic because energy is given back when bonds are made
What is bond enthalpy
The average energy required to break one mole of a stated bond
How do you work out the bond enthalpy
?H= energy products - energy react
So
?H = bonds broken - bonds made
Where ? means change in
If ?H = -ve, is the bond exothermic or endothermic
Exothermic as it had lost heat
If ?H = +ve, is the bond exothermic or endothermic
Endothermic because products have more energy than reactants
How does a endothermic energy profile diagram look
Energy of reactants (first line) is below energy of products (second line)
What does an exothermic energy profile diagram look like
Energy reactants (first line) is above energy of products (second line)
Which bit is the activation energy on a energy profile diagram
The distance from the first line to the peak of the graph
What is the energy absorbed on an energy profile diagram
The distance from the second line to the point at where the first line is
What are the 3 methods to find the enthalpy
1) ?H = Hproducts - Hreactants
2) ?H = bonds broken -bonds made
3) ?H = mc?t / h
1&2 are theoretic
3 is experimental
How do you work out the heat released
Q= MC?T
Q= heat release (joules)
?T= difference in temp. (T2-t1)
M=mass of water
C=specific heat capacity (418J per g per •c
