Energy in Bonds
If a system releases energy into the surroundings, how does the temperature change in the surroundings?
What type of reaction is this?
The temperature increases. This is an exothermic reaction.
The overall energy change in a chemical reaction is 63 kJ/mol. What does this tell us about the reaction.
This is an endothermic process.
True or False (if false, explain why): The more configurations particles can adopt in a given state, the less likely they will spend more time in that state.
False: The particles will be more likely to spend time in that state.
If the standard Gibb's free energy for a reaction is negative, what is the most likely interpretation of the reaction favorability?
This is an exothermic process, favoring the products.
When K is less than 1, are the reactants or products more favored?
the reactants are more favored
True or False (if false, explain why): Combustion reactions are examples of endothermic reactions whereas the decompositions of stable compounds are examples of exothermic reactions.
False: Combustion reactions are exothermic since energy is being released to form the bonds. Decomposition reactions are typically endothermic since energy is being absorbed to break the bonds
True or False (if false, explain why): Energetic stability increases with decreasing potential energy of a substance.
True
Determine the sign of ΔS for the following reactions:
1) the number of particles in a system decreases
2) the reactant changes from a gas to a liquid
1) -
2) -
The transformation of a system from one state to another, at constant temperature and pressure, is nonspontaneous if the Gibb's free energy:
increases, decreases, attains equilibrium, or remains constant
increases
For a reactant favored reaction, draw the concentration vs. time graph.
The reactants will start at a high concentration, gradually decreasing over time. The products will start at no concentration, gradually increasing over time. The two lines will never converge with the reactants being at a higher concentration than the products.
Which of the following bonds has the highest bond energy?
C-C, Si-Si, Ge-Ge, Sn-Sn
C-C
In the reaction of hydrogen with oxygen to make water, 1856 kJ of energy is taken in and 1370 kJ of energy is given out. Which of these statements can be concluded from this information?
The reaction is exothermic
The reaction is endothermic
The reaction has a high activation energy
The reaction is endothermic
For the substances below, choose the one with the higher molar So at 298 K:
CO (g) or H2 (g)
CO (g)
ΔH is negative, ΔS is negative. What is the nature of this reaction?
Draw the ΔG vs T graph for this reaction.
The reaction is spontaneous at low temperatures.
Graph: Starting at a negative ΔG, the slope line increases, crossing the x-axis, into positive ΔG as temperature increases.
For the reaction 2 SO2 (g) + O2 (g) <-> 2 SO3 (g), the equilibrium concentrations were found to be [SO3] = 5.0 x 10-2 M, [O2] = 3.5 x 10-3 M, and [SO2] = 3.0 x 10-3. What is the equilibrium constant for this reaction?
What is the directionality of this reaction at the equilibrium constant?
7.9 x 104 M
Reaction will be product favored.
The bond that has the higher bond energy is:
single bond between non-polar atoms
OR
single bond between polar atoms
single bond between polar atoms
What is the energy change for the reaction:
CH4 (g) + 2 O2 (g) --> CO2 (g) + 2 H2O (l)
(Bond energies: C-H = 415.5 kJ, O=O = 498 kJ, C=O = 805, O-H = 464 kJ)
-808 kJ/mol
Calculate the standard entropy of the following reaction:
CaCl2 (s) --> Ca2+ (aq) + 2 Cl- (aq)
(So = J/mol*K = Ca2+ = 154.89, CaCl2 = 104.6, Cl- = 56.5)
163.3 J/mol*K
At 50 oC, the reaction of ice and water has ΔH = 24 kJ/ mol and ΔS = -90 J/mol*K for the process H2O (s) --> H2O (l). What is the ΔG for the conversion of ice to liquid water?
What is the directionality of this reaction at 50 oC?
ΔG = 53.08 kJ
The reaction is endothermic, favoring the reactants.
Draw both the ΔG vs T and K vs T graphs for a reaction that is spontaneous in reverse for all temperatures.
What are the signs of ΔH and ΔS for this reaction?
ΔG vs T: The line will begin at positive ΔG, increasing with the temperature, remaining positive.
K vs T: The line will start at K < 1, logarithmically increasing with temperature, but always remaining K < 1
ΔH = +
ΔS = -
Which of these statements is true for the reaction profile of an exothermic reaction?
The reactants and products are at the same energy level
The reactants are at a higher energy level than the products
The products are at a higher energy level than the reactants
The reactants are at a higher energy level than the products
Calculate the enthalpy for the following:
HCCH + HCl --> H2CCHCl
(ΔHf in kJ/mol = HCCH = 227.4, HCl = -92.3, H2CCHCl = 37.3)
-97.8 kJ/mol
A reaction has the following PEC diagram analysis: The products on the left, upper side while the reactants are on the right, lower side.
Predict the signs of ΔH and ΔS. Is this reaction favoring the reactants or products more?
ΔH = +
ΔS = -
This reaction is endothermic, favoring the reactants more.
The ΔH and ΔS for a reaction at one atm are 42.322 kJ and 71 J/mol*K, respectively. At what temperature will ΔG be zero? What would be the nature of this reaction when above the found temperature?
596.1 K
Reaction will be product favored above this temperature.
What is the value of K for this aqueous reaction at 298 K? Is the reaction reactant- or product-favored?
A + B <-> C + D
ΔGo = - 67.23 kJ/mol
6.09 x 1011