Self Test on rates of reaction, equilibrium expressions, equilibrium constants, Le Chatelier's principle  

 Short essay questions

1.	What is a reversible reaction?

2.	Sketch the plot of reaction rate versus extent of reaction for reactants and products.
	Describe how the rate for the forward reaction changes with time.

	Describe how the rate for the reverse reaction changes with time.

3.	Write the equilibrium expressions for the following equations. Explain
	2 SO3 (g) <----> 2 SO2 (g) + O2 (g)

2 O3 (g) <----> 3 O2 (g)

	MgCO3(s) <----> CO2 (g) + MgO (s)
	C (s) + 2 Cl2 (g) <----> 2 CCl4 (g)

4.	Which of the following reactions has a positive entropy change and which has a negative
	one? Justify your answer.
	2 SO3 (g) <----> 2 SO2 (g) + O2 (g)

2 O3 (g) <----> 3 O2 (g)

	MgCO3(s) <----> CO2 (g) + MgO (s)
	C (s) + 2 Cl2 (g) <----> 2 CCl4 (g)

5.	A reaction has a DH = +5600 calories. The entropy change is -4.6 calories /Kelvin at 298
	Kelvin. Is this reaction spontaneous? Will raising the temperature ever make it spontaneous?

6.	An equilibrium reaction has the following equilibrium expression. Assume DH = -75,600 calories.
	K = [SO2 ]2 [O2 ] / [SO3]2
	What is the effect on [SO2 ] if the pressure is increased? What happens to [SO2 ] if the temperature is raised?

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7.	Give definitions for activation energy, heat of reaction, endothermic, exothermic, spontaneous reaction. What is the standard used for predicting spontaneous reactions?
	What effect does temperature have on reaction rates? Can an activation energy ever be negative? Explain your answer.

8.	The reversible reaction H2 (g) + Cl2 (g) <----> 2 HCl(g) has the equilbrium expression
	K = [HCl ]2/ [H2] [Cl2 ]
	The equilibrium mixture of reactants and products is illustrated. Based on the illustration which side of the equilibrium is favored, reactants or products? Is the value for the equilibrium constant greater than "1"? If you added 24 H2 and 24 Cl2 molecules to an empty container, how many H2 and Cl2 molecules would remain when the reaction reached equilibrium? Would the HCl molecules out number the Cl2 and H2 molecules?

Multiple choice

1.	Which of the following pairs of bonds is the weakest?
	a. Cl and Cl
	b. H and H
	c. Br and Br
	d. F and F

2.	Which of the following has a positive entropy change?
	a. formation of a liquid from a gas
	b. formation of a solid from a gas
	c. formation of a solid from a liquid
	d. 4 SO3(g)----> 4 SO2(g) + 2 O2(g)

3.	Which of the following single bonds is most reactive?
	a. H and H
	b. Br and Br
	c. F and F
	d. C and C

4.	Which of the following equilibrium constants has the biggest relative amount of products?
	a. K = 1
	b. K = 0.0005
	c. K = 2,000
	d. K = 0

5.	What is true for a spontaneous reaction?
	a. enthalpy change is always + positive
	b. free energy change is always + positive
	c. entropy change is is always - negative
	d. free energy change is always - negative

6.	Endothermic reactions can never be spontaneous
	a. true
	b. false

7.	An equilibrium constant changes when the concentration of reactants is raised.
	a. true
	b. false

8.	Which of the following reactions is irreversible?
	a. 2 SO3 (g) <----> 2 SO2 (g) + O2 (g)
	b. 2 O3 (g) <----> 3 O2 (g)
	c. MgCO3(s) <----> CO2 (g) + MgO (s)
	d. 2 C6H6(l) + 15 O2(g) <----> 12 CO2 (g) + 6 H2O (g)

9.	Which of the following has an equilibrium expression with a only a "1" in the denominator?
	a. 2 O3 (g) <----> 3 O2 (g)
	b. MgCO3(s) <----> CO2 (g) + MgO (s)
	c. C (s) + 2 Cl2 (g) <----> 2 CCl4 (g)
	d. 2 SO3 (g) <----> 2 SO2 (g) + O2 (g)

10.	A catalyst alters the rate of a reaction because
	a. it has weak bonds
	b. it weakens a bond in reactants and changes the activation energy for the reaction
	c. it lowers the activation energy for the forward reaction but not the reverse reaction
	d. decreases the value for the equilibrium constant

Dr. Walt Volland,