Equilibrium aned kinetics

Essential Questions: What is chemical equilibrium Essential Questions: What is chemical equilibrium? What are the types of chemical equilibrium? Chemical equilibrium: 1. When the rates of the forward and reverse reactions are equal. 2. State of balance 3. No net change occurs in the actual amount of the compounds in the system. Ex: 2SO2(g) +O2(g)  2SO3(g) 2:1:2 4. Dynamic state (both reactions continues), do not stop. 5. Represented by : or  6. Occurs only in a closed system

What is going on here? N2O4  2NO2 A FORWARD reaction goes from left to right (toward 2NO2). A REVERSE reaction goes from right to left (toward N2O4)

It is a two-way reaction: Observe the double arrow. The reaction is reversible. N2O4(colorless)  2NO2(brown) Molecules are constantly going back and forth between the two compounds.

Observe the reaction between H2 and I2: 1 mole H2 1 mole I2 2 moles of HI The reaction is reversible. Observe the double arrow.

Reversible reaction-conversion of reactants to the products and conversion of the products to the reactants occurs simultaneously. Ex: 2SO2(g) + O2(g)2SO3(g) forward reaction 2SO2(g) + O2(g)  2SO3(g) reverse reaction OR 2SO2(g) + O2(g) 2SO3(g) 

Over time, the concentrations reach the same levels regardless of the initial amounts. At equilibrium, the amounts of products are constant (but not equal).

Shifting… C A D B A + B   C + D A B C D Shift to the right (more products): A B C D Shift to the left (more reactants): A B C D

An example of chemical equilibrium: The Haber process for making ammonia: N2 + 3H2  2NH3 + 92 kJ Ammonia (NH3) is being made at the same rate as it is being turned back to N2 and H2. Amounts of NH3, H2, and N2 remain constant. Ammonia production critical to agriculture

Types of equilibrium: Phase Equilibrium Solution Equilibrium 1. Exists between the liquid and the solid phase. 2. Exists between the MP of the solids phase and the FP of the liquid phase. Ex: H2O (s) H2O (L)

Solution Equilibrium: 1. When the rate of dissolving and the rate of recrystallization are equal. 2. Solution is saturated Exs.: C12H22O11(s) C12 H22 O11(aq) CO2(g) CO2(aq)

Equilibrium Position: 1. Relative concentration of the reactants and the products at equilibrium 2. Indicates whether the reactants or the products are favored. Exs: A  B Forward reaction favored formation of B A  B Reverse reaction favors the formation of A. 3.Length of arrows indicates which reaction is favored.

Essential Questions: what is Le Chatelier’s Principle Essential Questions: what is Le Chatelier’s Principle? What is the effect of different stresses on a system at equilibrium? Le Chatelier’s Principle-if a stress is applied to a system in dynamic equilibrium, the system changes in a way that relieves the stress. Stresses Include: Concentration Product and Concentration Reactants Change in Temperature Change in Pressure Catalyst

Concentration : 1. Change in concentration of the products or reactants disturbs equilibrium 2. System adjusts to minimize the effect of the change. Exs. H2CO3(aq)CO2(aq) + H2O (L) 3. New equilibrium, will be established When a reactant is removed, the reaction shifts in the direction of the formation of the reactants. When a reactant is added, the reaction shifts in the direction of the formation of the products.

Temperature: 1. Increasing the temperature, causes the equilibrium to favor the endothermic reaction. Ex: 2SO2(g) + O2 2SO3(g) + heat 2. Removal of heat favors the exothermic reaction Ex: 2SO2(g) + O2 + heat 2 SO3(g)

Pressure: 1. Affects a system only in gaseous equilibrium that have an unequal number of moles of reactants and products. 2. Increase in pressure always favors the lower number of moles. Ex: N2(g) + 3H2(g) 2NH3(g) 3. Decrease in pressure favors the higher number of moles. Ex: N2(g) + 3H2(g)  2NH3(g)

Our example: N2 + 3H2  2NH3+ 92kJ Effect on equilibrium Endothermic rxn. Favored. Shift LEFT. Exothermic reaction favored. Shift RIGHT. Make more NH3 to compensate. Shift RIGHT. Makes more N2 to compensate. Shift LEFT. Makes more N2 and H2 to compensate. Shift LEFT. favors NH3 (less space required). Shift RIGHT. Favors N2 and H2 (more space allowed). Shift LEFT. Stress: Increase Temperature Decrease temperature Increase [N2] Increase [H2] Decrease [N2] Increase [NH3] Increase pressure Decrease pressure

. Common Ion – an ion that is found in both salts in a solution Ex: PbCrO4(s) Pb+2 (aq) + CrO4-2(aq) Addition of lead nitrate or sodium chromate, would cause a shift to the left to produce more PbCrO4

2. Measured in amount of reactant changing per unit of time. Essential Question: What are reaction rates, the collision theory and an activated complex? Reaction Rates; 1. Measure of the spread of any change that occurs within an interval of time. 2. Measured in amount of reactant changing per unit of time. Collision Theory: 1. Atoms/ions/ molecules can form products when they collide with each other if they have sufficient kinetic energy. 2. Particles without sufficient kinetic energy bounce apart unchanged.

Activation Energy-minimum energy that colliding particles must have in order to react. Activated Complex: 1. Temporary intermediate product that may break apart and reform the reactants or rearrange that atoms and form new products the atoms and form new product. 2. Unstable arrangement of atoms Forms at the peak of activation energy 4. In existence only briefly (10-13 seconds)

Potential Energy Diagrams –illustrate the potential energy that occurs during a chemical reaction

What is Energy of reaction? Energy gained or lost in a chemical change. 20 kJ are gained in this reaction.

Factors Affecting Reaction Rates: Temperature Concentration Essential Questions: What are the four factors that affect the rate of a reaction? How does each factor affect the rate? Factors Affecting Reaction Rates: Temperature Concentration Particle Size Use of Catalyst

Temperature: 1. Usually increasing temperature will increase rate of reactions. 2. Will increase the number of collisions and kinetic energy of the particles. Concentration- An increase in the number of particles in a given volume, will increase the rate of the reaction. Ex: Crowded room

What does an endothermic reaction look like? Energy is a reactant A + B + energy  C + D Energy is taken in from the surroundings. Products contain more energy than the reactants.

What is Energy of reaction? Energy gained or lost in a chemical change. 20 kJ are gained in this reaction.

What does an Exothermic reaction look like? Energy is a product A + B  C + D + Energy Energy given off to the surroundings. Products contain less energy than the reactants. Beaker gets hot or gives off light or heat.

Energy is lost in this chemical reaction. It exothermic.

Particle Size: 1. Total surface area of particles affects the rate of the reaction. 2. The smaller the particles, the larger the surface area for a given mass, thus an increase in the amount of reactants exposed for a reaction to occur. Ex: Granulated sugar versus lump of sugar

Catalyst: Substance that increase the rate of a reaction. 2. Permits reactions to occur at a lower energy level, thus decreasing the activation energy needed. 3. Not a reactant or a product Ex: 2H2(g) + O2(g)  2H2O(L) 4. Unchanged in the reaction Inhibitor-substance that interferes with the action of a catalyst

What does a catalyst do? It lowers the energy barrier. ← It is now easier to get over the hill. More particles have this amount of energy so more can react.

Kinetics – the study of how fast and how much

Essential Questions: What is entropy? How do you use Table I? Enthalpy : Heat of reaction Measure in kJ at STP 3. Table I In exothermic reactions , the potential energy of the products is lower than that of the reactants. In endothermic reactions, the potential energy of the products is greater than that of the reactants. Melting and evaporation are endothermic phases changes. Condensation and freezing are exothermic phase changes. The greater the negative H , the more stable the products of the reaction. The greater the positive H, the more unstable the products of the reaction.

A plot of Energy versus time for a chemical reaction: DH = heat Of reaction Potential Energy PE of products PE of Reactants Progress of reaction  In this case, energy is released (exothermic)

A plot of Energy versus time for a chemical reaction: DH = heat Of reaction Potential Energy PE of products PE of Reactants Progress of reaction  In this case, energy is absorbed (endothermic)

What is Heat of Reaction? PE of products Potential Energy DH = heat of reaction DH= H(products) – H(reactants) PE of Reactants Progress of reaction  Heat of reaction is the heat gained or lost in a reaction. It is the difference between Products’ Energy and Reactants’ Energy

What is activation energy? ACTIVATED COMPLEX- highest energy reached. ACTIVATION ENERGY is the energy required to get a reaction started. It is the energy to get over the hill.

Where do I put the activation energy? Potential Energy DH = heat Of reaction DH= H(products) – H(reactants) Progress of reaction  Activation energy is the energy required to initiate (start) a reaction.

What is the effect of a catalyst? Our catalyst is an enzyme↓ A catalyst lowers the energy hill. It lowers the ACTIVATION ENERGY. The catalyst is not consumed in the reaction.

Reactions are reversible: Activation energy for reverse (R L) reaction. Activation Energy (forward) Potential Energy DH= heat of reaction Progress of reaction  Activation energy is the energy required to initiate (start) a reaction.

Reference Table I

Entropy: 1. Measure of disorder of system Ex: Clean room -low entropy Messy room -high entropy Solids-low entropy Gases high entropy 2. Increase in entropy favors the spontaneous chemical reaction 3. Decrease in entropy favors the non-spontaneous reaction.

Law of Disorder- natural tendency for systems to move in the direction of maximum disorder or randomness Spontaneous reaction: 1. Occurs naturally 2. Favors the formation of the products at the specified conditions 3. Releases energy. Ex: fireworks

Nonspontaneous reactions-1 Nonspontaneous reactions-1.Doesn’t favor the formation of products under specified conditions. 2. Ex: H2CO3(aq) CO2(g) + H2O(l) <1% >99% 99% of H2CO3 is converted to products in the forward reaction, thus it is spontaneous and releases energy In the reverse reaction, CO2(g) + H2O(l), less that 1% combines to form H2CO3, thus nonspontaneous. In most reversible reactions, 1 reaction is favors over the other

In every chemical reaction, heat is either release or absorbed and entropy or randomness either is increased or decreases. The size and direction of the enthalpy changes and entropy changes together determine whether a reaction is spontaneous; that is. Whether if it favors the products and releases energy.