Thermodynamics, Kinetics and Equilibrium

Word DefinitionEffective collision A collision between reactant particles that results in a chemical reaction taking

place.Reaction rate The amount of reactant consumed or product formed per unit of time.Catalyst A substance that is added to a reaction to increase the reaction rate by

decreasing the activation energy without being consumed itself.Heat of reaction H – heat of the products minus heat of reactants. Activation energy The energy that must be added to the reactants to allow them to react.Activated complex intermediate stage in a reaction between reactants and productsEntropy A system’s state of disorder or randomness. Spontaneous A change that, once started, continues the rest of the way on its own.Nonspontaneous A change that requires a constant input of energy to occur.Equilibrium A condition where the rate of the forward change equals the rate of the reverse

change.Enthalpy H – same as heat of reaction

Energy of Chemical Reactions A. Chemical Kinetics

1. Chemical Kinetics relates to movement of reacting particles2. Explain the collision theory of reactions

a.) Chemical change may occur when reactant particles collide. b.) The relative particle velocity must be large to produce an effective collision.c.) The particles must collide with proper alignment to product a chemical

change3. Account for the factors that affect reaction rates: nature of reactants, surface area,

concentration, temperature of reacting system, presence of a catalyst a.)Nature of reactants

o Ionic compounds react faster than covalent/molecular compoundsb.) Surface area

o Solids only react on their surfaceo Smaller solid particles have more surface area per gram

Powder will react faster than chunks c.) Concentration

o Solid and liquid reactants have a constant concentrationo Solutions and gases have variable concentrationso The greater the concentration of mobile particles the greater the

probability of collision Faster rate of reactiond.) Temperature

o Temperature equals the average kinetic energy of the systemo An increase in temperature increases the rate of ALL chemical

reactionso Higher temperature causes a greater frequency of collisionso Higher temperature causes greater percentage of collisions

occurring with sufficient energy – effective collisionse.) Catalyst

o A catalyst lowers the activation energy required to start the reactiono A catalyst increases the rate of all chemical reactions (both forward

and reverse reactions)o A catalyst is not consumed during a chemical reaction

f) Pressureo Pressure only effects gaseso An increase in pressure reduces the volume of a gas and acts like

an increase in concentration of that gas, which will increase the effective collisions (and therefore reaction rate)

B. Thermodynamics 1. Thermodynamics relates to transfer of energy between kinetic energy and

potential energy.2. Interpret potential energy diagrams

a.) Potential energy diagramso The symbol “H” is the change in enthalpy, or heato H reaction= [H products ] – [H reactants]o The reaction is labeled an endothermic reaction if the energy of

products is greater than reactants – energy is absorbedo H is positive for endothermic reactions

o The reaction is labeled an exothermic reaction if the energy of reactants is greater than products – energy is released

o H is negative for exothermic reactionso A graph may be used to show energy changes during a chemical

reaction.

3. Interpret significance of changes of heat in chemical or physical changes using Reference Table I

a.) If H is negative – heat is released = Exothermic (note at bottom of Table I "a minus sign indicates an exothermic reaction”)

b.) If H is positive –heat is absorbed = Endothermic4. Describe the role of changes in entropy on chemical and physical changes

a.) Entropy is randomness or disorderb.) High temperature favors large entropiesc.) Low temperature favors low entropies

d.) Entropy is related to the phase of matter-Solids have low entropy –Gases have high entropy

e.) An increase in total entropy of a system favors a spontaneous changeC. Chemical Equilibrium

1. During chemical equilibrium the rate of a forward reaction is equal to the rate of a reverse reaction. (The concentrations of the products and reactants are constant NOT equal)

2. Le Chatelier's Principle states that when a stress is placed on a system that system will shift in a direction to relieve that stress. The reaction will shift Away from any Added stress, and Towards any stress Taken or removed.

a) Stresseso Pressure

For solid and liquid systems changes in pressure have no effect

Pressure affects some systems containing gases The side with more moles of gas is the one being stressed If there is an equal amount of moles of gas on both sides

the reaction is not stressedo Temperature

o The side of the reaction containing energy is the one that is stressed

o Concentrationo An increase in the concentration of any reactant causes the

reaction to shift toward the product side and vice versao A decrease in the concentration of species causes the

reaction to shift toward that specieso Catalysto A catalyst affects both sides of a reaction equally, so it is not a

stress

1) Kinetics Homework

1) Explain how the following will affect the reaction rate (increase, decrease, remains the same):

a) Adding N2 (g) to the reaction N2 + 3 H2 2 NH3 (g) _____________________

b) Removing H2 (g) from the reaction N2 + 3 H2 2 NH3 (g) _____________________

c) Increasing the pressure on the reaction N2 (g) + 3 H2 (g) 2 NH3 (g) _____________________

d) Using powdered NaCl instead of large crystal NaCl in a reaction _____________________

e) Adding water catalyst to a double replacement reaction _____________________

f ) Increasing pressure on Na (s) + ZnSO4 (aq) Na2SO4 (aq) + Zn (s) _____________________

2) Place three 5.0 gram samples of sugar in three different 50.0 mL samples of pure water in three different insulated cups, all at 50.0 oC. Sample A is a single cube of sugar, Sample B is granulated sugar and Sample C is powdered sugar. Which sample will dissolve slowest? Explain.

3) Place three identical 5.0 g cubes of sugar into three different 50.0 mL samples of pure water in three different insulated cups. Cup A contains water at 20oC, Cup B contains water at 10oC and Cup C contains water at 40oC. In which cup will the sugar dissolve fastest? Explain.

2) Potential Energy Diagrams Homework

1) Rewrite the following reactions from Reference Table I, placing the energy on the appropriate side:

Reaction Rewritten with Energy on the Correct SideN2 (g) + 3 H2 (g) 2 NH3 (g)

N2 (g) + 2 O2 (g) 2 NO2 (g)

H2 (g) + I2 (g) 2 HI (g)

2) For the same reactions above, indicate if they are endothermic or exothermic and also indicate whether the products are stable or unstable.

Reaction Exothermic or Endothermic?

N2 (g) + 3 H2 (g) 2 NH3 (g)

N2 (g) + 2 O2 (g) 2 NO2 (g)

H2 (g) + I2 (g) 2 HI (g)

3) For the following blank PE Diagram, sketch the shape of an endothermic curve and label the Hreactants, Hproducts, Hactivated complex, activation energy and H. You do not have to put any numbers in.

4) For the following blank PE Diagram, sketch the shape of an exothermic curve and label the Hreactants, Hproducts, Hactivated complex, activation energy and H. You do not have to write any numbers in.

5) For the following PE Diagram, answer the questions below:

1) What is the heat of reactants?a) 20 kJ b) 50 kJ c) 90 KJ d) 30 kJ

2) What is the heat of the products?a) 20 kJ b) 50 kJ c) 90 KJ d) 30 kJ

3) What is the heat of the activated complex?a) 20 kJ b) 50 kJ c) 90 KJ d) 30 kJ

4) What is the activation energy for this reaction?a) 90 kJ b) 70 kJ c) 30 KJ d) 40 kJ

5) What is the H of this reaction?a) + 30 kJ b) – 30 kJ c) +70 kJ d) -70 kJ

6) Draw a dashed line on the above diagram to indicate what the graph would look like if a catalyst was added to this reaction.

7) What type of reaction is this?a) exothermic b) endothermic c) both d) neither

6) For the following PE Diagram, answer the questions below:

1) What is the heat of reactants?a) 30 kJ b) 110 kJ c) 140 KJ d) 160 kJ

2) What is the heat of the products?a) 30 kJ b) 110 kJ c) 140 KJ d) 160 kJ

3) What is the heat of the activated complex for the uncatalyzed reaction?a) 30 kJ b) 110 kJ c) 140 KJ d) 160 kJ

4) What is the activation energy for the catalyzed reaction?a) 30 kJ b) 110 kJ c) 140 KJ d) 160 kJ

5) What is the H of this reaction?a) + 80 kJ b) – 80 kJ c) +130 kJ d) -130 kJ

6) Draw a dashed line on the above diagram to indicate what the graph would look like if a catalyst was added to this reaction, using the catalyzed reaction line as your guide.

7) What type of reaction is this?a) exothermic b) endothermic c) both d) neither

7) For the following PE Diagram, what does each arrow represent?

a) Heat of Reactants ________

b) Heat of Products ________

c) Activation Energy ________

d) H ________

e) Heat of Act. Cmplx ________

f) Sketch a dashed line to indicate the effect of adding a catalyst.

3) Will A Reaction Happen On Its Own Once Started? Homework

1) Does entropy increase or decrease in the following phase changes and reactions? Are these favored or unfavored changes?

Reaction Entropy Increase or Decrease?

CO2 (s) CO2 (g)

I2 (g) I2 (s)

C (s) + O2 (g) CO2 (g)

4 Al (s) + 2 O2 (g) 2 Al2O3 (s)

2 CO (g) + O2 (g) 2 CO2 (g)

2 H2 (g) + O2 (g) 2 H2O (l)

2) Water freezes only at temperatures of 0oC and below.

a) Is this an increase or decrease in entropy?_____________________________________

b) When water freezes, is this exothermic or endothermic?__________________________

3) You have a NiMH AAA rechargeable battery in your mp3 player. After a while, the battery indicator shows that the battery is losing its charge (running out of “juice”) and needs to be recharged, which you do by placing the battery into a recharger and plugging it into the outlet in your room. After a few hours, the charger shows that the battery is now full, so you take it out and put it back in your mp3 player and rock to the tunes.

a) Is discharging the battery endothermic or exothermic? Why?

b) Is recharging the battery endothermic or exothermic? Why?

4) Equilibrium Systems Homework

1) find the heat of reaction for the following and indicate whether they are endothermic or exothermic:

a) 2 H2 (g) + O2 (g) 2 H2O (g) _______________________________________________

b) N2 (g) + 3 H2 (g) 2 NH3 (g) _______________________________________________

c) 2 C (s) + H2 (g) C2H2 (g) _______________________________________________

2) In your opinion, why does the system have to be closed at equilibrium? Please demonstrate thought in your answer.

3) What has to be equal at equilibrium?a) the mass of the products and reactantsb) the volume of the products and reactantsc) the concentration of the products and reactantsd) the rates of formation of the products and reactants

4) A stoppered bottle contains 20 grams of liquid water and 20 grams of water vapor. Does equilibrium exist?

a) Yes, the amount of each component is equalb) Yes, the bottle is stopperedc) Only if the rates of evaporation and precipitation are equald) Only if all three of the above are true

5) What word is used to describe a solution at equilibrium?a) saturated b) unsaturated c) supersaturated d) wet

5) Changing Equilibrium Homework

A) 2 NH3 (g) + heat N2 (g) + 3 H2 (g)

1) Stress: increase in [N2]. Direction of Shift:________________________ What is the resulting effect on the concentration of:

a) [NH3]________________________

b) [H2]_________________________

2) Stress: increase in temperature Direction of Shift:________________________ What is the resulting effect on the concentration of:

a) [N2]_________________________

b) [NH3]________________________

3) Stress: increase in pressure Direction of Shift:________________________ What is the resulting effect on the: a) number of moles of N2______________________

b) number of moles of NH3_____________________

B) 2 NO (g) N2 (g) + O2 (g) + heat

4) Stress: decrease in [O2] Direction of Shift:________________________ What is the resulting effect on the concentration of:

a) [N2]_________________________

b) [NO]_________________________

5) Stress: decrease in temperature Direction of Shift:________________________ What is the resulting effect on the concentration of:

a) [O2]_________________________

b) [NO]_________________________

6) Stress: increase in pressure Direction of Shift:________________________ What is the resulting effect on the:

a) number of moles of O2______________________

b) number of moles of NO______________________

C) Complete the following questions:

Given the equilibrium N2 (g) + 3 H2 (g) 2 NH3 (g) + heat :

a) If N2 is added to the system at equilibrium, which direction will the equilibrium shift?

1. Forward 2. Reverse

b) If H2 is removed from the system at equilibrium, which direction will the equilibrium shift?

1. Forward 2. Reverse

c) If NH3 is added to the system at equilibrium, which direction will the equilibrium shift?

1. Forward 2. Reverse

d) If temperature is decreased to the system at equilibrium, which direction will the equilibrium shift?

1. Forward 2. Reverse

e) If pressure is increased to the system at equilibrium, which direction will the equilibrium shift?

1. Forward 2. Reverse

f) If H2 is removed from the system at equilibrium, what will happen to the concentrations of (circle your choice for each)1. N2 {increase} {decrease} {remain the same}

2. NH3 {increase} {decrease} {remain the same}

g) If NH3 is removed from the system at equilibrium, what will happen to the concentrations of (circle your choice for each)

1. N2 {increase} {decrease} {remain the same}

2. H2 {increase} {decrease} {remain the same}

D) Given the equilibrium system H2 (g) + I2 (g) + 53.0 kJ 2 HI (g), list four things that can be done to result in an increase in the concentration of HI (g).

E) Given the equilibrium system NaOH (s) Na+1 (aq) + OH-1 (aq) + 44.51 kJ, list four things that can be done to result in an increase in the concentration of NaOH (s).