Reaction Kinetics and Reaction Kinetics and Equilibrium Equilibrium

How compounds react with each How compounds react with each otherother

Collision Theory Collision Theory

A reaction is most likely to occur if A reaction is most likely to occur if reactant particles collide with the reactant particles collide with the proper energy and orientationproper energy and orientation

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Reaction Rate Affecting Reaction Rate Affecting Factors Factors

• Nature of ReactantsNature of Reactants• Concentration Concentration • Surface Area Surface Area • Temperature Temperature • Presence of a CatalystPresence of a Catalyst• Pressure for Gases Pressure for Gases

Nature of Reactants Nature of Reactants

Factors that contribute to reaction Factors that contribute to reaction rate:rate:

- Electronegativity - Electronegativity

- Ionization energy - Ionization energy

- Atomic Radius. - Atomic Radius.

Bonding on Rate of Bonding on Rate of ReactionReaction

Covalent bondsCovalent bonds require more energy during require more energy during collisions due to a greater number of bonds collisions due to a greater number of bonds needed to be broken and reformed. needed to be broken and reformed.

Ionic BondsIonic Bonds are faster to react and require less are faster to react and require less energy during a collision.energy during a collision.

Concentration Concentration

We measure concentration by the number of We measure concentration by the number of moles there are in a L of solution (Molarity). moles there are in a L of solution (Molarity).

More moles = more collisions More moles = more collisions

Ex: Burning paper. When the oxygen concentration Ex: Burning paper. When the oxygen concentration is low the paper burns slowly. Raise the amount of is low the paper burns slowly. Raise the amount of oxygen the paper burns faster. oxygen the paper burns faster.

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Surface Area Surface Area

The larger the surface area the easier it The larger the surface area the easier it is to react because there are more is to react because there are more chances for collision.chances for collision.

Temperature Temperature

• The average kinetic energy of molecules The average kinetic energy of molecules in a compound. in a compound.

• The more molecules move the higher The more molecules move the higher the temperature. the temperature.

• Higher temperature results in more Higher temperature results in more collisionscollisions

Presence of a Catalyst Presence of a Catalyst

AA substance whose presence increases substance whose presence increases the rate of a chemical reaction.the rate of a chemical reaction.

Catalysts change (decrease) the Catalysts change (decrease) the activation energy which increases the activation energy which increases the rate of reactionrate of reaction

Activation Energy Activation Energy

Activation energy is the minimum Activation energy is the minimum energy required to initiate a reaction.energy required to initiate a reaction.

When particles collide with the right When particles collide with the right amount of amount of activation energyactivation energy it breaks it breaks the existing bond. the existing bond.

Energy Energy

• Kinetic EnergyKinetic Energy (motion) – this the energy of work (motion) – this the energy of work being done being done

• Potential EnergyPotential Energy (static) – the potential for (static) – the potential for something to do worksomething to do work

**Remember that there are many types of energy: **Remember that there are many types of energy: - electrical - electrical - thermal- thermal- mechanical- mechanical- electromagnetic - electromagnetic - nuclear- nuclear

Endothermic vs. Endothermic vs. Exothermic Reactions Exothermic Reactions

• ExoExothermic (thermic (exexit) reactions give off heat it) reactions give off heat energy during a chemical reaction energy during a chemical reaction

• EndoEndothermic (thermic (enenter) reactions absorb ter) reactions absorb heat energy during a chemical reaction heat energy during a chemical reaction

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Potential Energy Diagram Potential Energy Diagram

Used to show the energy released or stored in endothermic and Used to show the energy released or stored in endothermic and exothermic reactionsexothermic reactions

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Reading Energy Diagrams Reading Energy Diagrams

• THE Y AXISTHE Y AXIS – Potential energy of the – Potential energy of the reaction reaction

• THE X AXISTHE X AXIS – Reaction as it takes place – Reaction as it takes place over time over time

• CURVE CURVE – Represents the potential – Represents the potential energy at each step of a chemical energy at each step of a chemical reactionreaction

Reading Energy Diagrams Reading Energy Diagrams

• EXOTHERMIC REACTION – energy given off EXOTHERMIC REACTION – energy given off during a reaction during a reaction

LOOK AT THE CURVE AND SEE IF IT ENDS LOOK AT THE CURVE AND SEE IF IT ENDS AT A LOWER VALUEAT A LOWER VALUE

The energy of the products is lower than the The energy of the products is lower than the energy of the reactantsenergy of the reactants

Reading Energy DiagramsReading Energy Diagrams

• ENDOTHERMIC – energy is absorbed during a reaction ENDOTHERMIC – energy is absorbed during a reaction

• The energy of the products is higher than the heat of the The energy of the products is higher than the heat of the reactantsreactants

LOOK AT THE CURVE AND SEE IF IT ENDS AT A LOOK AT THE CURVE AND SEE IF IT ENDS AT A HIGHER VALUEHIGHER VALUE

• ACTIVATION ENERGY – The amount of energy needed to ACTIVATION ENERGY – The amount of energy needed to reach the peak of the curvereach the peak of the curve

SUBSTRACT THE ENERGY AT THE PEAK OF THE SUBSTRACT THE ENERGY AT THE PEAK OF THE CURVE FROM THE INITIAL ENERGY CURVE FROM THE INITIAL ENERGY

Effect of a Catalyst of Effect of a Catalyst of Activation EnergyActivation Energy

Catalysts ContinuedCatalysts Continued

• A catalyst lowers the activation A catalyst lowers the activation energy required for the reaction to energy required for the reaction to occur. By lowering the activation occur. By lowering the activation energy, the chemical reaction can energy, the chemical reaction can occur much more quickly.occur much more quickly.

Reversible ReactionsReversible Reactions

• Not all reactions go completely to Not all reactions go completely to completion (all reactants are used completion (all reactants are used up)up)

• Instead, some reactions can occur Instead, some reactions can occur both forward and reverse at the both forward and reverse at the same time. A reversible reaction is same time. A reversible reaction is symbolized by double arrowssymbolized by double arrows

• 2SO2SO22(g) + O(g) + O22(g) 2SO(g) 2SO33(g)(g)

Equilibrium Equilibrium

The rate at which the products are The rate at which the products are formed is at the same rate that the formed is at the same rate that the reactants are formed.reactants are formed.

Equilibrium is represented with a double Equilibrium is represented with a double arrow. Example: arrow. Example:

EquilibriumEquilibrium

Entropy Entropy

The measure of the randomness or The measure of the randomness or disorder of a system’s energy. disorder of a system’s energy.

The greater the randomness the The greater the randomness the greater the entropy. greater the entropy.

Entropy of Substances Entropy of Substances

As a substance goes from solid to liquid As a substance goes from solid to liquid to gas, entropy increases. to gas, entropy increases.

Systems in nature tend to undergo Systems in nature tend to undergo changes toward low energy and high changes toward low energy and high entropy (they want to lose energy and entropy (they want to lose energy and gain freedom)gain freedom)

Change of State (review)Change of State (review)

• A change of state, also called a A change of state, also called a phase change, is the conversion of phase change, is the conversion of a substance from one of the 3 a substance from one of the 3 states of matter to another. A states of matter to another. A change of state always involves a change of state always involves a change in energy. change in energy.

Heating and Cooling Heating and Cooling CurvesCurves

• Shows how a substance changes Shows how a substance changes states at each temperature states at each temperature increase over time.increase over time.

Animation

Phase DiagramPhase Diagram

Equilibrium ReviewEquilibrium Review

• Some chemical reactions are Some chemical reactions are reversiblereversible

• When a reaction is occurring both When a reaction is occurring both forward and reverse at the same forward and reverse at the same rate, equilibrium is reachedrate, equilibrium is reached

• Example: Example:

NN22 + 3 H + 3 H2 2 2 NH 2 NH33 + energy + energy

Le Chatlier’s PrincipleLe Chatlier’s Principle

• When a system at equilibrium is When a system at equilibrium is subjected to a stress (a change in subjected to a stress (a change in concentration, temperature, or concentration, temperature, or pressure), the equilibrium will shift pressure), the equilibrium will shift in the direction that tends to in the direction that tends to counteract the effect of the stress.counteract the effect of the stress.

Video

Le Chatlier’s PrincipleLe Chatlier’s Principle

• Example: Example:

NN22 + 3 H + 3 H2 2 2 NH 2 NH33 + energy + energy

If the concentration of Nitrogen is If the concentration of Nitrogen is increased, the reaction will shift to increased, the reaction will shift to the right and favor the products the right and favor the products side, making more ammonia and side, making more ammonia and giving off more heat.giving off more heat.

Le ChatlierLe Chatlier

• Example: Example:

NN22 + 3 H + 3 H2 2 2 NH 2 NH33 + energy + energy

If the temperature is increased, the If the temperature is increased, the reaction will shift to the left and reaction will shift to the left and favor the reactants side, making favor the reactants side, making more N and Hmore N and H

Effect of Pressure on Effect of Pressure on EquilibriumEquilibrium

• Example: Example:

NN22 + 3 H + 3 H2 2 2 NH 2 NH33 + energy + energy

(4 moles gas)(4 moles gas) (2 moles gas) (2 moles gas)

If the pressure is increased, the If the pressure is increased, the reaction will shift to the right, reaction will shift to the right, favoring the side with the lower favoring the side with the lower number of moles of gasnumber of moles of gas

Heat and TemperatureHeat and Temperature

• Heat (J or calories) – a transfer of energy from a Heat (J or calories) – a transfer of energy from a body of higher temperature to a body of lower body of higher temperature to a body of lower temperature. Thermal energy is associated temperature. Thermal energy is associated with the random motion of atoms and with the random motion of atoms and molecules. molecules.

• Ex) steam v waterEx) steam v water• Temperature – a measure of the average Temperature – a measure of the average

kinetic energy of the particles of a substance. kinetic energy of the particles of a substance. Temperature is not a form of energy. Temperature is not a form of energy.

• Question: What state of matter has the most Question: What state of matter has the most energy? GASenergy? GAS

Heat CalculationsHeat Calculations

• Specific Heat Capacity – the amount Specific Heat Capacity – the amount of energy required to raise the of energy required to raise the temperature of a substance one temperature of a substance one degree. degree.

• Ex: Takes more energy to heat a Ex: Takes more energy to heat a swimming pool than a cup of waterswimming pool than a cup of water

• Specific heat Capacity of H2O (l) = Specific heat Capacity of H2O (l) = 4.18 J/g X C4.18 J/g X C

Calculations conCalculations con

• Fusion – meltingFusion – melting• Heat of Fusion – the amount of Heat of Fusion – the amount of

heat needed to convert unit mass heat needed to convert unit mass of a substance from a solid to a of a substance from a solid to a liquid at constant temperature. liquid at constant temperature.

• - when ice is melting the kinetic - when ice is melting the kinetic energy stays the sameenergy stays the same

• Heat of Fusion of H2O = 334 J/gHeat of Fusion of H2O = 334 J/g

Calculations conCalculations con

• Heat of Vaporization – the amount of Heat of Vaporization – the amount of heat needed to convert a unit mass heat needed to convert a unit mass of a substance from a liquid to a gas of a substance from a liquid to a gas at constant temperature. at constant temperature.

• - when ice is boiling the kinetic energy - when ice is boiling the kinetic energy stays the samestays the same

• Heat of V of H2O = 2260 J/gHeat of V of H2O = 2260 J/g

• TABLE B in Reference TableTABLE B in Reference Table

Calculations con.Calculations con.

• Q = mCQ = mC∆T∆T

• Q = mHfQ = mHf

• Q = mHvQ = mHv

Vapor PressureVapor Pressure

• In every liquid, some particles are far enough In every liquid, some particles are far enough away from each other to be considered gas away from each other to be considered gas but are pushed down by atmospheric but are pushed down by atmospheric pressure. When in liquid, some particles are pressure. When in liquid, some particles are far enough apart to escape their neighboring far enough apart to escape their neighboring molecules and enter the gas phase (vapor). molecules and enter the gas phase (vapor). As temperature increases, particles gain As temperature increases, particles gain more energy and more particles escape from more energy and more particles escape from the surface. The pressure these gaseous the surface. The pressure these gaseous particles exert is called vapor pressure. As particles exert is called vapor pressure. As temp increases, vapor pressure increases. temp increases, vapor pressure increases.

Vapor Pressure con. Vapor Pressure con.

• Vapor pressure eventually builds Vapor pressure eventually builds up enough to equal atmospheric up enough to equal atmospheric pressure. When it surpasses pressure. When it surpasses atmospheric pressure, the liquid atmospheric pressure, the liquid boils and allows the gaseous boils and allows the gaseous particles to escape. particles to escape.

• Vapor PressureVapor Pressure – pressure gaseous – pressure gaseous particles exert upwardparticles exert upward