2. Warm-Up 01/04/2017
A mixture of gases (NO2,CO2, SO2) is collected in a bottle. The partial pressure of NO2 is atm, and the partial pressure of CO2 is atm. If the total pressure of the gases is atm, what is the partial pressure of SO2?
A) 2.89 atm
B) 7.32 atm
C) 9.23 atm
D) atm

3. Unit 6 Energy, Rates of Reaction and Equilibrium

4. Energy
Energy is the ability to do work, produce heat, or cause change
Units: joule (J), kilojoule (kJ), calorie (cal)
1000 cal = 1 Calorie/(Kilocalorie)
1 cal = J
Convert 45 calories to joules.

5. Heat (q)
Heat (q) is the energy that flows from warm objects to cool objects
Heat, like diffusion, flows from HIGH to LOW concentrations

6. Specific Heat (Cp)
Specific Heat (Cp) is the amount of heat required to raise the temperature of one gram of that substance by one degree Celsius
Units:

7. Specific Heat (Cp)

8. Specific Heat
q = heat; Unit: Joules
m= mass; Unit (in grams)
Cp = specific heat; Unit ( J / (g * ºC)
Δt = change in temperature; Unit (ºC)

9. Specific Heats
Substance: Specific Heat:
Water (l)
Water (s) (ICE)
Aluminum
Iron

10. Signs for “q”
If energy is absorbed, the sign for “q” is +
If energy is released, the sign for “q” is –
Ex) A substance absorbs 300 kJ of heat
Ex) Water loses 345 kJ of heat when it freezes

11. Example #1
The temperature of a sample of iron with a mass of 10.0 g changed from 50.4ºC to 25.0ºC. What amount of energy was released? The specific heat of iron is J / (g * ºC).

12. Examples
2) How much energy is absorbed when a 501 g sample of water is heated from 51ºC to 55ºC?

13. Example
3) How much energy is released when 2.34 g of Aluminum (specific heat = J / (g * ºC)) is cooled from 75ºC to 34ºC?

14. Phase Diagrams
Phase Diagrams are a graph of pressure versus temperature that shows in which phase a substance exists under different conditions
Triple Point: point at which all three phases of matter coexist

16. Words that corresponding to the Phase Diagram
Freezing-is the process in which a liquid turns into a solid when cold enough
Melting- is a process that results in the phase change of a substance from a solid to a liquid.
Condensation-is the change of the physical state of aggregation (or simply state) of matter from gaseous phase into liquid phase

17. Continued
Vaporization-of an element or compound is a phase transition from the liquid phase to gas phase
Sublimation-of an element or compound is a transition from the solid to gas phase with no intermediate liquid stage.
Deposition-an element or compound is a transition from the gas to solid phase with no intermediate liquid stage.

18. Warm-Up 5/12/2015
Which example indicates that a chemical change has occurred?
A. When two aqueous solutions are mixed, a precipitate is formed.
B. As ammonium nitrate dissolves in water, it causes the temperature of the water to decrease.
C. Alcohol evaporates when left in an open container.
D. Water is added

19. Heating & Cooling Curves
Heating and cooling curves show the change in temperature (avg. Kinetic energy) over time as a substance is heated or cooled

21. Phase Diagrams
Heat of Fusion: the energy required to completely convert a solid into a liquid
Water’s Heat of Fusion (ΔHfus) = 334 J / g
q = m * Hfus
How much energy is required to melt a 3.4 g ice cube?

22. Phase Diagrams
Heat of Vaporization: the energy required to completely convert a liquid into a gas
Water’s Heat of Vaporization (ΔHvap) = 2260 J / g
q = m * Hvap
How much energy is required to boil 25.6 g of water?

23. Review
How much energy is required to completely melt 200 grams of snow?

24. Energy If a reaction releases energy, it is exothermic
If a reaction requires energy, it is endothermic

25. Exothermic Reaction

26. Endothermic Reaction

27. Using Energy Graphs
If the products are higher in energy than the reactants, then reaction is endothermic
If the reactants are higher in energy than the products, the reaction is exothermic

28. Reaction Rates
A reaction rate measure the changes that occur within intervals of time
Reaction rates refer to the time that it takes for a reaction to occur
For any reaction to occur, the correct amount of energy must be present

29. Collision Theory
The collision theory states that new bonds are formed when particles collide
These particles must have the right amount of energy so that they “stick” together when they collide and form a chemical bond

30. Collision Theory
If particles do not have the correct amount of energy, the particles will NOT stick together and form a chemical bond

31. Factors That Affect Reaction Rates
Factors that affect rate of reaction:
Temperature
Concentration
Particle Size
Catalysts

32. Temperature’s Effect on Rxn Rates
As temperature is increased, the particles that compose substances speed up and gain more energy
Generally, the higher the temperature, the more collisions between particles of reactants
The more collisions between particles, the faster products are formed

33. Effect of Concentration
A higher concentration of a substance means that more particles are present
Therefore the reaction will occur faster at higher concentrations

34. Effect of Particle Size
Particle size is related to surface area
The larger the particles of a substance, the larger the surface area of the substance
A larger surface area means that the particles will come in contact with other particles
The smaller the particle size, the faster a reaction will occur

35. Effect of Catalysts
Catalysts are substances that participate in the reaction but are not affected by the reaction
Catalysts serve to speed up a chemical reaction by reducing the amount of activation energy
*Inhibitors are substances that slow the reaction down considerably

36. Warm-Up 5/7/2015
Which pair of elements would most likely bond to form a covalently bonded compound?
A) Sodium and Fluorine
B) Barium and Chlorine
C) Phosphorus and Oxygen
D) Magnesium and Sulfur

37. Equilibrium We have seen reactions proceed from reactants to products
Many reactions are reversible
A reversible reaction occurs when enough of the product has been formed that the product begins to break down and form reactants

38. Equilibrium
A reversible reaction is symbolized by double arrows
2 SO2
+ O2
2 SO3
Equilibrium occurs when the rate of the forward reaction equals the rate of the reverse reaction

39. Equilibrium Equilibrium is defined in terms of concentration
Once at equilibrium, the concentration of reactants and products does not change
If one of the double arrows is drawn larger than the other one, the longer arrow indicate the favored side of the reaction

40. Equilibrium Continued
Equilibrium is a balance between the rate of the forward reaction and the reverse reaction

41. Equilibrium Expressions
Equilibrium expressions (Keq) is the ratio of the concentration of products divided by concentration of reactants
The expression is always products divided by reactants

42. Setting Up Equilibrium Expressions
mA + nB  sC+ rD
The equilibrium expression is:
Keq = products / reactants
[C]s * [D]r
Keq=
[A]m * [B]n

43. Interpreting Equilibrium Expressions
The symbol [ ] means molar concentration
The exponents in the expressions are the coefficients for the balanced equation
The units for Keq is not generally used

44. Write Equilibrium Expressions
1. N2O4  2NO2
2. H2 + I2  2HI
3. N2 + H2  NH3
4. BrCl  Br2 + Cl2

45. Solving Equilibrium Problems
1. What is the value for the Keq when 0.1 M H2 reacts with 0.5 M O2 to produce 0.5 M H2O?
First, write balanced equation
Second, write Keq expression
Third, substitute values in the expression and solve

46. Warm-Up 5/7/2015
The half-life of phosphorus-32 is days. How many milligrams of a mg sample of phosphorus-32 will remain after days?

47. Determine the value for Keq
2) 4 M N2 reacts with 6 M H2 to produce 10 M NH3

48. Practice
3) 5 M CO2 breaks down to produce 6 M CO and 3 M O2 in an equilibrium reaction

49. Practice
1. An equilibrium mixture at 425C is determined to consist of 3.5 x 10-2 M of H2, x 10-3 M of I2 and 2.55 x 10-2 M of HI. The Balanced Equation is
H2+ I2  2 HI

50. Warm-Up 5/8/2015
An equilibrium mixture at 500 ˚C is determined to consist of 5 M of H2, 3 M CS2, 1.5 M of CH4 and 1 M of H2S.
The balance equation is:
4 H2 + CS2  CH4 + 2 H2S

51. LeChatelier’s Principle
LeChatelier’s Principle predicts shifts in equilibrium due to changes in the system
LeChatelier’s Principle states that if a stress is applied to a system, the equilibrium will shift to relieve that stress

52. Example of Shifts in Equilibrium
PCl5  PCl3 + Cl2 ∆H = kJ
What would happen if the following stresses are applied:
1. Addition of PCl5
2. Removal of Cl2
3. Addition of Catalyst
4. PCl3 is removed
5. Temperature is increased

53. Other Stresses in Equilibrium
Pressure: any pressure changes affect only the gaseous substances in a reaction
An increase in pressure favors the side of the equilibrium with the smallest number of gaseous particles
A decrease in pressure favors the side with the largest amount of gaseous particles

54. Example with Pressure
N2 (g) + 3 H2 (g)  2 NH3 (g)
Predict which side of the equilibrium will be favored if:
a) the pressure is increased
b) the pressure is decrease

55. Example Problem
Predict how the equilibrium will shift for the following:
H2 + I2  2 HI
a. If more H2 is added
b. If I2 is removed
c. If the pressure is increased

56. Enthalpy
Enthalpy-is the internal warmth of a substance due to the motion of its particles and is symbolized by H
Enthalpy is the energy that is released when an exothermic reaction occurs or the required energy in an endothermic reaction

57. Enthalpy Continued
Possible Units for Enthalpy: Joules (J) or calories (cal)
If H has a negative value, the reaction is exothermic
If H has a positive value, the reaction is endothermic

58. Using Enthalpy
If the reaction has a negative H, energy is a product; if H is positive, energy is a reactant
1. C + O2  CO2, H= kJ
2. C + O2  CO2, H= kJ

59. Rewrite the following reactions using energy as a product or reactant
2 NaHCO3  Na2CO3 + H2O + CO2, H= +129 kJ
CaO + H2O  Ca(OH)2, H= kJ
CH4 + 2O2  CO2 + 2 H2O H= kJ

60. Entropy
Entropy is the law of disorder states that things move in the direction of the maximum disorder or randomness.
Entropy (S) is the measure of the disorder of a system
The disorder in the universe is increasing

61. Entropy
If S is positive, there is an increase in entropy or disorder
If S is negative, there is a decrease in entropy or disorder
Gases are the most disordered state of matter
Solids are the least disordered state of matter

62. Decide if the following show an increase or decrease in entropy:
1. The melting of ice cream
2. Making a sandwich
3. The freezing of water
4. The decomposition of HCl
5. The reaction between Mg and Zn(OH)2
6. The formation of H2O from H2 and O2