Kinetics/ Reaction Rates

Transcription

1 Reaction Rates Kinetics/ Reaction Rates Expressing Reaction Rate Collision Theory 1) Chapter 17 2) 3) Jodi Grack; Wayzata High School; Plymouth, MN Reaction Rates activated complex Factors Affecting Reaction Rate Nature of Reactants activation energy Concentration Surface Area * Spontaneity implies Jodi Grack; Wayzata nothing High School; Plymouth, about MN reaction rate. 1

2 Factors Affecting Reaction Rate Temperature Factors Affecting Reaction Rate Catalysts Reaction Spontaneity Reaction Spontaneity Reaction Spontaneity Predicting ΔH: spontaneous reaction Reactions occur due to two driving forces: 1) Predicting ΔS: 2) Jodi Grack; Wayzata High School; Plymouth, MN Jodi Grack; Wayzata High School; Plymouth, MN 2

3 Reaction Spontaneity Directions: A) For each reaction, indicate which direction is favored by min. Energy/max. randomness. B) For each reaction, assuming products are favored, what is the driving force? C) Which reaction below has the greatest tendency to form products? Jodi Grack; Wayzata High School; Plymouth, MN 1) NH 4 NO Reaction Spontaneity NO 3 (s) NH NH 4 + (aq) (aq) + NO - 3 (aq) ; ΔH H = +27 kj 2) N 2 (g) + 3 H 2 (g) NH 3 (g) + heat 3) NO 3 + heat NO 2 (g) + 1/2 O 2 (g) 4) 2HI (g) 5) C 3 H 8 (g) H 2 (g) + I 2 (g) ΔH H = -26 kj + 5 O 2 (g) 3 CO 2 (g) + 4 H 2 O (l) Jodi Grack; Wayzata High School; Plymouth, MN Reaction Spontaneity Equilibrium 6) CO (g) + O 2 (g) CO 2 (g) ; ΔH H = -x x kj 7) H 2 SO 4 (l) H+ (aq) + HSO - 4 (aq) + heat 8) H 2 O (s) 9) H 2 O (g) H 2 O (l) H 2 O (l) Jodi Grack; Wayzata High School; Plymouth, MN 3

4 Equilibrium Video Notes Chapter 18 Chemical Equilibrium 1. How do we recognize equilibrium? 2. How do we explain equilibrium? At the beginning of the reaction Reactant Concentrat ions Forward Reaction Rate Product Concentrat ions Reverse Reaction Rate Throughout the course of the reaction At equilibrium Examples of Equilibrium 3 Factors that Liquid/Vapor Equilibrium affect a. What are the two opposing forces? Equilibrium b. How can we recognize the system is at equilibrium? 1) c. What would happen if the system were heated? 2) Solubility equilibrium a. What are the two opposing forces? 3) b. How can we recognize the system is at equilibrium? c. What would happen if more solid were added to the system? Chapter 18 Chemical Equilibrium Law of Chemical Equilibrium a given temperature, a chemical system may reach a state in which a particular ratio of reactant and product concentrations has a constant value. aa + bb cc + dd Chemical equilibrium ex. Fe 3+ (aq) + SCN - (aq) FeSCN 2+ (aq) (Note: FeSCN 2+ is a colored ion.) a. What are the two opposing forces? b. How can we recognize the system is at equilibrium? 4

5 Chapter 18 Chemical Equilibrium Chapter 18 Chemical Equilibrium Interpreting the value of K: K (very large) K Reaction H 2 (g) + I 2 (g) 2HI K expressio n Value K Rxn/side favored? N 2 (g) + 3 H 2 (g) 2 NH 3 (g) K (very small) Mg(OH) 2 (s) Mg 2+ (aq) + 2 OH - (aq) 2 NO 2 (g) N 2 O 4 (g) Chapter 18 Chemical Equilibrium Reaction K expression Value K Rxn/side favored? Determining the Value of the Equilibrium Constant H 2 (g) + I 2 (g) 2 HI(g) K = If at equilibrium [H 2 ] = M [I 2 ] = M [HI] = M Fe 3+ (aq) + SCN- (aq) FeSCN 2+ (aq) 0.97 K =? 5

6 Determining the Value of the Equilibrium Constant 1) H 2, I 2, and HI were put into a reaction vessel and all had an initial concentration of 1.00 M. When equilibrium was established, it was found that the concentration of HI was M. What must be the equilibrium concentrations of the H 2 and I 2? H 2 (g) + I 2 (g) 2 HI(g) (all units = M) M Determining the Value of the Equilibrium Constant 2) H 2 and I 2 were put into a reaction vessel so their initial concentrations were 1.00 M and 2.00 M respectively. When equilibrium was established, it was found that the concentration of HI was 1.88 M. What must be the equilibrium concentrations of the H 2 and I 2? H 2 (g) + I 2 (g) 2 HI(g) (all units = M) Determining the Value of the Equilibrium Constant 3) H 2 and I 2 were put into a reaction vessel. When equilibrium was established, it was found that the concentration of H2 was M and the concentration of HI was 4.20 M. What must be the equilibrium concentration of I 2? H 2 (g) + I 2 (g) 2 HI(g) M? 4.20 M 6

7 Determining the Value of the Equilibrium Constant 4) A and B react according to the balanced equation below to produce D and E. The initial concentrations of A and B were both 5.00 M. When equilibrium was established, the concentration of C was M. What are the equilibrium concentrations of all the other substances? What is the value of the equilibrium constant? A (g) + 2 B (g) 2 C (g) + 3 D (g) Factors Affecting Equilibrium LeChatelier s Principle Types of Stresses LeChatelier Demo Factors Affecting Equilibrium Demo Summary Shifting: (Concentration changes addition/removal of reactants or products.) 1. The equilibrium will shift (TOWARD or AWAY FROM) what is added. 2. The equilibrium will shift (TOWARD or AWAY FROM) what is taken. Shifting: (Temperature changes.) The equilibrium will shift (TOWARD or AWAY FROM) what is added. The equilibrium will shift (TOWARD or AWAY FROM) what is taken. Shifting: (Pressure changes as a result of a volume change.) NOTE: Really just another concentration. INCREASING PRESSURE, as a result of a volume change, will favor the side of the reaction with GREATER or FEWER gas molecules. DECREASING PRESSURE, as a result of a volume change, will favor the side of the reaction with GREATER or FEWER gas molecules. 7

8 Factors Affecting Equilibrium Demo Summary Value of the equilibrium constant: The value of the equilibrium constant will change when (CONCEN.'S, TEMP'S, PRESSURES) are changed. K will increase any time. K will decrease any time. Solubility Equilibrium BaSO 4 (s) Ba 2+ (aq) + SO 4 2- (aq) K large (>10) K ~ 1 K small (<0.10) Solubility Determining Solubility (Given Ksp) STEPS 1. Write the dissolving equation for the compound 2. Let s = the concentration of the compound that can dissolve 3. Write the equilibrium law expression 4. Plug the value of K and the ion concentrations (in terms of s) into the expression and solve for s. Determining Solubility (Given Ksp) 1) What s the solubility of AgI? (Ksp = 8.5 x ) 8

9 Determining Solubility (Given Ksp) 2) What s the solubility of Mg(OH) 2? (Ksp = 5.6 x ) Determining Solubility (Given Ksp) 3) What s the solubility of Ag 2 CO 3? (Ksp = 8.5 x ) Determining Ksp (Given Solubility) STEPS 1. Write the dissolving equation for the compound 2. Determine the concentration each ion given the solubility 3. Write the equilibrium law expression 4. Plug the ion concentrations into the expression and solve for Ksp. Determining Ksp (Given Solubility) 1) What s the Ksp for AgCl? (Solubility = 1.3 x 10-5 M) 9

10 Determining Ksp (Given Solubility) 2) What s the Ksp for PbCl 2? (Solubility = 1.6 x 10-2 M) Determining Ksp (Given Solubility) 3) What s the Ksp for AgCl? ([Ag + ] = in a saturated solution.) 10