Unit 9 - Thermodynamics Flashcards
State the first law of thermodynamics
Energy can not be created or destroyed it can only be transferred or converted from one form to another
What is the internal energy
All of the energy that is in a closed system
What is the equation for internal energy
Define the terms of this equation
Delta U = q + w
q = heat added to the system (J) W = work done J
If W is positive what does this mean
Work is done to the system
If W is negative what does this mean
The system does wrk
What is the equaion for work done by a system
Define the terms
W = - Pext x deltaV
Pext = 1.01x10^5 V = volume
What is temperature
A measure of the avaerage kinetic energy of the atoms or molecules in the system
q =
Mc delta T
Define the terms of q = mcdeltaT
q= heat m = mass c = specific heat capacity T = temp
What is the specific heat capacity
Energy required to raise 1kg of a substance by 1 deg
What is Cm / Cmol
The energy required to raise 1 mole of a substance by 1 degree
Work doene is
Movement against a force
Eqn for work done
W=fd
What happens when a gas does work
Increase in volume and work done is negatice
What happens when work is done on a gas
Decrease in the volume and work done on a gas is positive
What is the equation for Pressur
P = FA
What is the equation for work relating pressure, area and displacement
Work = Pressure x Area X Displacement
Work = P X Change in volume
Molecules always move toward a
lower energy state
Equation for enthalpy
Define the terms
H = U + PV
H = enthalpy U = internal energy P = pressure V = volume
Hess’s Law states …
The total enthalpy change for a chemical reaction does not depend on the pathway it takes, it only depends on the initial and final states
What is the standard enthalpy change of formation
Ammount of heat lost or gained when one mole of a compound is formed from its consitiuent elements
Exothermic –>
Heat is released
Increase in the temperature of the surroundings
Endothermic –>
Heat is absorbed
Temperature of the surroundings decreases
What is bond enthalpy
The energy it takes to break one mole of bonds in the gaseous phase
Breaking a bond …
Always requires energy
Making a bond …
Always releases energy
Define entropy
The ammount of dissorder in a system
A box with 8 balls has ________ entropy than a box of 6 balls
More
What is the second law of thermodynamics `
Any spontaneous reaction will increase the disorder of the universe
An increase in entropy during a reaction means that
Products are more disordered than the reactants
What is Gibbs Free Energy
Is the ammount of energy in a system that is available to do useful work
What is the free energy of an element in its standard state
0
Delta G =
Delta H - T . Delta S
G = free energy H = enthalpy T = absolute temp (K) S = entopy
If delta H is greater than T delta S …
reaction is enthalpy driven
If T delta S is greater than delta H …
Reaction is entropy drive
How spontaneous is the following reaction
Delta H is less than 0 AND
Delta S is greater than zero
Reaction is spontaneous at all values of T (T can only be positive)
Delta S =
Delta S products - delta S reactants
Negative delta S means
Entropy is higher in the reactants than the products
Order is increasing –> DECREASE IN DISORDER
How spontaneous is the following reaction
Delta H is less than 0 AND
Delta S is less than 0
Spontanous only a low values of T
When TdeltaS is SMALL
How spontaneous is the following reaction
Delta H is greater than 0
Delta S is greater than 0
Spontaneous at large values of TdeltaS
When TdeltaS is large
How spontaneous is the following reaction
Delta H is greater than 0 AND
Delta S is less than 0
Non spontaneous at all values of T
deltaG > 0
If deltaS is positive this means …
give an example of whn this would be the case
Positive value of deltaS when entropy increases
Example when we have more moles of gaseous products than reactants
what happens when deltaH is positive
Energy is released in the form of heat
If delta G < 0 this means
Spontaneous
If delta G > 0 this means
Not spontaneous in the forward direction
A spontaneous reaction is AKA
Exergonic
A non spontanous reaction AKA
Endeegonic
At G=0 the system is as
equilibrium
What does adiabatic mean
No heat is added or taken away
equation for delta S in terms of heat and temperature
Delta S = Q/T
Q = heat T = temperature
All spontanous reactions are
Irreversible
Give another equation for delta G
Define the terms of this eqn
Delta G = Delta G0 + RTlnQ
Q = reaction quotient, eqbm contant before the reaction has reached eqbm
How would you determine Q
COnc products / conc reactants
