Energetics Flashcards
(39 cards)
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
What is equilibrium
It is when the system is balanced
? = reversible reaction. Goes forward and backwards at the same time. Eg ice melting ? water freezing
What are the two types of equilibrium
- Static equilibrium
- Dynamic equilibrium
Define static equilibrium
When equilibrium is achieved and there is no net movement
Define dynamic equilibrium
When do you rate (speed) of the forward reaction is equal to the rate of the reverse. The net change is zero. Note: if the forward reaction is endothermic, the reverse reaction is exothermic
What must happen for there to be a reversible reaction
- It must be a closed system
- (In dynamic) the rates of both ways of the reaction must be equal
What is the Le chatelier principle
When a change is exerted on a system (chemical reaction) in dynamic equilibrium, the POE moves to do the exact opposite
What is the POE affected by
- Temperature
- Concentration of reactants
- Pressure of reactants
What will increase in temperature due to the position of equilibrium
It will move to the endothermic side which absorbs heat.
What will increase the concentration due to the position of equilibriums
It will move from left to right to remove excess reactants
