Terms and Laws
Enthalpy
Entropy
Gibbs Free Energy
Calculations
100
The definite part or area being studied.
System
100
What letter is used to represent enthalpy?
ΔH
100
How can you tell if entropy has increased?
Look at the changes in state of matter and/ or the number of moles
100
The entropy and enthalpy of a reaction are both negative. Is the reaction spontaneous?
The reaction will be spontaneous if and only if the magnitude of the enthalpy is greater than the magnitude of the entropy times the temperature.
100
Which of the following is a true statement regarding the energy involved in the formation of Methane, CH4, from graphite C(s) and H2(g) ?
a. Energy will be released, then consumed
b. Energy will be consumed, then released
b. Energy will be consumed, then released
200
The energy that includes all of the potential and kinetic energy of all the parts of the system
Internal energy
200
Which type of reaction releases heat?
Exothermic reaction
200
What is the symbol for entropy?
ΔS
200
What happens when ΔG is zero?
The system is at equilibrium
200
A→E+F ΔH=−50kJ
E+F→C+G ΔH=+85kJ
B+G→D ΔH=−10kJ
What is the change in enthalpy for the given reaction?
A+B→C+D
+25 kJ
300
What type of reaction is thermodynamically favored?
Spontaneous reaction
300
Two ways to calculate Enthalpy?
ΔH(total) = ∑ΔH(products) - ∑ΔH(reactants)
ΔH(total) = ∑ Bonds broken - ∑ Bonds formed
300
A reaction is spontaneous when the system has (negative or positive) entropy?
positive
300
Describe a reaction that can never be spontaneous
The entropy decreases and the enthalpy increases
300
The following is a list of specific heat capacities for a few metals.
Ccopper=0.385
Ciron=0.444
Csilver=0.240
Caluminum=0.900
A 50g sample of an unknown metal is heated with 800 joules. If the temperature of the metal increases by 41.6oC, what is the identity of the unknown metal?
Copper
400
What is the Second Law of Thermodynamics?
Any irreversible process results in an overall increase in entropy, where as a reversible process results in no change in entropy.
400
N2(g) ΔHf=0kJ
O2(g) ΔHf=0kJ
NO ΔHf=90kJ
What is the enthalpy of the following reaction?
N2(g)+O2(g)→2NO
180 kJ/mol
400
Increase in temperature causes increase or decrease in entropy? Why?
Increase in entropy because molecules become more disordered and move faster
400
Suppose that a reaction with an equilibrium constant equal to 4.5∗106 occurs while at standard state conditions. Is the Gibbs free energy positive or negative?
The Gibbs free energy change for this reaction is negative and the reaction is spontaneous.
400
The following list is the enthalpies of formation for the compounds:
ΔHC3H8=−103.85kJmol
ΔHCO2=−393.5kJmol
ΔHH2O=−241.82kJmol
If one mole of propane is burned, what is the enthalpy of the reaction?
−2044 kJ
500
What does Hess's law state?
The total enthalpy change for the reaction is the sum of all changes.
500
The surrounding decreases in temperature when this reaction takes place
Endothermic reaction
500
Define entropy?
The extent of disorder in a system.
500
Suppose that a reaction has ∆H = -28 kJ and ∆S= -60 J/K. At what temperature will it
change from spontaneous to non-spontaneous?
a. 467 K
b. 50 k
c. 500 K
d. 46.7 K
467 k
500
Cice=0.5cal/g∘C
Cwater=1.0cal/g∘C
ΔHfusion=80 cal/g
How much energy is needed to raise the temperature of five grams of ice from −10 C to 35 C?
600cal