Warm-Up 01/04/2017
• A mixture of gases (NO2,CO2, SO2) is collected
in a bottle. The partial pressure of NO2 is 1.25
atm, and the partial pressure of CO2 is 2.63
atm. If the total pressure of the gases is 11.20
atm, what is the partial pressure of SO2?
• A) 2.89 atm
• B) 7.32 atm
• C) 9.23 atm
• D) 11.20 atm
Unit 6
Energy, Rates of Reaction and Equilibrium
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 = 4.184 J
•Convert 45 calories to joules.
Heat (q)
•Heat (q) is the energy that flows from warm
objects to cool objects
•Heat, like diffusion, flows from HIGH to LOW
concentrations
J
g * °C
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:
J
g * °C
J
g * °C
Specific Heat (Cp)
q = m*c p * Dt
J
g * °C
Dt = t final - tinitial
Specific Heat
•q = heat; Unit: Joules
•m= mass; Unit (in grams)
•Cp = specific heat; Unit ( J / (g * ºC)
•Δt = change in temperature; Unit (ºC)
Specific Heats
•Substance:
•Water (l)
•Water (s) (ICE)
•Aluminum
•Iron
Specific Heat:
4.184
2.03
0.897
0.449
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
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 0.449 J / (g * ºC).
Examples
•2) How much energy is absorbed when a 501
g sample of water is heated from 51ºC to
55ºC?
Example
•3) How much energy is released when 2.34 g
of Aluminum (specific heat = 0.897 J / (g *
ºC)) is cooled from 75ºC to 34ºC?
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
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
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.
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
Heating & Cooling Curves
• Heating and cooling curves show the
change in temperature (avg. Kinetic
energy) over time as a substance is
heated or cooled
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?
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?
Review
• How much energy is required to completely melt
200 grams of snow?
Energy
• If a reaction releases energy, it is exothermic
• If a reaction requires energy, it is endothermic
Exothermic Reaction
Endothermic Reaction
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
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
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
Collision Theory
• If particles do not have the correct amount of
energy, the particles will NOT stick together and
form a chemical bond
Factors That Affect Reaction Rates
• Factors that affect rate of reaction:
• Temperature
• Concentration
• Particle Size
• Catalysts
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
Effect of Concentration
• A higher concentration of a substance
means that more particles are present
• Therefore the reaction will occur faster at
higher concentrations
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
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
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
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
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
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
Equilibrium Continued
• Equilibrium is a balance between the rate of the
forward reaction and the reverse reaction
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
Setting Up Equilibrium Expressions
• mA + nB  sC+ rD
• The equilibrium expression is:
• Keq = products / reactants
Keq=
s
[C]
r
[D]
*
m
n
[A] * [B]
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
Write Equilibrium Expressions
• 1.
• 2.
• 3.
• 4.
N2O4  2NO2
H2 + I2  2HI
N2 + H2  NH3
BrCl  Br2 + Cl2
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
Warm-Up 5/7/2015
•The half-life of phosphorus-32 is 14.30 days.
How many milligrams of a 20.00 mg sample
of phosphorus-32 will remain after 85.80
days?
Determine the value for Keq
•2) 4 M N2 reacts with 6 M H2 to produce 10 M
NH3
Practice
• 3) 5 M CO2 breaks down to produce 6 M CO and 3 M
O2 in an equilibrium reaction
Practice
• 1.
An equilibrium mixture at 425C is
determined to consist of 3.5 x 10-2 M of H2, 1.75
x 10-3 M of I2 and 2.55 x 10-2 M of HI. The
Balanced Equation is
H2+ I2  2 HI
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
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
Example of Shifts in Equilibrium
• PCl5  PCl3 + Cl2 ∆H = - 45.6 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
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
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
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
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
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
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= -393.5 kJ
•2. C + O2  CO2, H= + 393.5 kJ
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= -65.2 kJ
CH4 + 2O2  CO2 + 2 H2O H= -890.4 kJ
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
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
Decide if the following show an increase or
decrease in entropy:
•1.
•2.
•3.
•4.
•5.
•6.
The melting of ice cream
Making a sandwich
The freezing of water
The decomposition of HCl
The reaction between Mg and Zn(OH)2
The formation of H2O from H2 and O2