Thermodynamics (w7) Flashcards
What are the 4 forms of potential energy ?
- gravitational (a raised weight)
- elastic (a stretched rubber band)
- chemical (a charged battery)
- electrical (a mobile phone which is switched off)
Define potential energy …
Any form of stored energy
What are the 5 forms of kinetic energy ?
- radiant (electric toaster)
- thermal (boiling water)
- sound (buzzing bee)
- electrical (desk lamp)
- mechanical (bowling ball rolling)
Define kinetic energy …
The energy of moving objects.
What is a system ?
The substance in the flask
What are the three types of system ?
-closed system
-open system
-isolated system
What is the zeroth law of thermodynamics ?
“If two systems are in thermal equilibrium with a third system, the two original systems are in thermal equilibrium with each other”
What is the first law of thermodynamics?
“Energy cannot be created or destroyed – it can only be transformed from one form to another”
What is the law of conservation of energy ?
“The change in internal energy of a closed system will be equal to the heat added or released by the system minus the work done by the system on its surrounding or the work done on the system by its surroundings”
What is the equation for the first law of thermodynamics ?
Delta U = Q - W
Change in internal energy = heat added to the system - work done by the system
What does it mean when the volume is constant ?
It is isovolumetric
-delta U = q
-no works done on or by the system
-any energy change is a result of heat transfer
What does is mean if there is a constant temperature ?
It is isothermal
-q = w
- no change in internal energy
- any heat transferred to system is used to do work
What does it mean if no heat is transferred ?
It is adiabatic
-delta A = W
- internal energy changed only for work Dione or received by the system.
Define heat capacity …
Heat Capacity (C): amount of heat required to raise a substance’s temperature by 1 Kelvin
Define specific heat capacity …
Specific Heat Capacity (Cₛ): amount of heat required to raise 1 gram of a substance by 1 Kelvin
What is an endothermic process ?
When energy is gained
(Temp of unit increases so deltaH is POSITIVE)
What is an exothermic process ?
When energy of unit is lost to surroundings
(It looses energy so temp decreases, deltaH is NEGATIVE)
What is the second law of thermodynamics ?
‘’ the universe is always moving towards the maximum disorder’’
What happens if there is an increase in the number of microstates ?
The entropy of the system increases (Wf>Wi)
So deltaS >0.
What happens if there is a decrease in the number of microstates ?
The entropy of the system will decrease (Wf<Wi) so deltaS<0.
What is the order of entropy for states ?
Solid < liquid < gas
E.g melting solid increases entropy then Vaporising this increases entropy even more.
What effect does increasing temperature have on entropy ?
The entropy will be greater as molecules gave more kinetic energy and therefore more dispersion.
What effect does mixing of particle types have on entropy ?
It increases the entropy therefore dissolution increases entropy.
What is the third law of thermodynamics ?
“At absolute zero (0 K), the entropy of a perfect, crystalline substance is zero”
When does a system come to equilibrium ?
When it reaches minimum Gibbs energy
What does equilibrium constant K describe ?
The composition of a reaction mixture when it comes to equilibrium
What is thermodynamic activity ?
Effective measured concentration or pressure of a component at a given moment (equilibrium for k)
When is K used ?
In heterogeneous reactions
- when a reaction has more than one phase - instead of using Kc or Kp, K is used.
What must K always be associated with ?
A specified temperature and the equation of the reaction being considered.
What is the reaction quotient (Q)?
Reaction Quotient Q: Measure of the composition of the reaction mixture as the reaction progresses – not at equilibrium
What happens If ∆Gr < 0, Q < K ?
Then the forward reaction proceeds
What happens if ∆Gr > 0, Q > K ?
Then the reverse reaction proceeds
What happens If ∆Gr = 0, Q = K ?
Then the system is at equilibrium
When does a reaction go to completion ?
If delta G is more -ve than -22.8 kj/mol
What is Le Chatelier’s principle `/
When a change is made to a system in dynamic equilibrium, the system responds to minimise the effect of the change
