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

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:

Specific Heat (Cp)

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: Specific Heat: Water (l) 4.184 Water (s) (ICE) 2.03 Aluminum 0.897 Iron 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 [C]s * [D]r Keq= [A]m * [B]n

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. N2O4  2NO2 2. H2 + I2  2HI 3. N2 + H2  NH3 4. 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. 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