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Regents Chemistry
KINETICS
What is Kinetics?
Kinetics is the branch of chemistry that deals with rates of chemical reactions
Different factors affect how quickly chemical reactions occur
In order for a reaction to occur, reactant particles must collide This is called COLLISION THEORY
Reactions occur between collisions of particles that are orientated correctly and have sufficient amounts of energy-ACTIVATION ENERGY!!!!!
1- Correct orientation2- Sufficient activation energy!!!
1- Wrong orientation or not enough activation energy.
2- ACTIVATION ENERGY: the minimum amount of energy needed to form the activaion complex and start a reaction. : Kinetic energy is converted to potential energy
Why is Kinetics Important?
Kinetics allows chemists to predict how fast a reaction will occur
Important in the synthesis of all kinds of compounds
In manufacturing, it is essential to making products, timing rates between chemical
reactions to get a desired product
What Factors Affect Rate of Reaction?
The rate of a chemical reaction depends on a number of factors that affect the number of effective collisions between particles Nature of Reactants Concentration Surface Area Pressure Temperature Presence of a Catalyst
Nature of Reactants
Reactions involve the breaking of existing bonds and the formation of new bonds
Generally, covalently bonded substances are slower to react than ionic substances as they have move bonds to be broken Breaking more bonds requires that the
particles must have more energy when they collide
Concentration
Most chemical reactions will proceed at a faster rate if the concentration of one or more of the reactants is increased
Ex: Combustion of Paper Normal air is 20% oxygen, if we use pure
oxygen it burns much faster! Why? KMT says that more collisions
between oxygen and paper particles = faster rate of reaction!
1- The greater concentration of reactants, the more collisions
2- Increase concentration = increase collisions = increase rate of reaction!!! Chemical reaction is faster!!!
TEMPERATURE
1- Increase in temperature = increase in rate of reaction
2- WHY?
ANS: increase in kinetic energy and motion of particles- more collisions of particles
Surface Area
When more surface area of a substance is exposed, there are more chances for reactant particles to collide
Ex: one centimeter of a cube of Mg reacting with HCl reacts more slowly then increasing the surface area by breaking Mg down into smaller pieces
INCREASING SURFACE AREA
Pressure
Pressure has little or no effect on rates of reactions between liquids and solids…
It does have an effect on gases!An increase in pressure has the
effect of increasing the concentration of gaseous particles Therefore, it increases the rate of a
reaction that involves only gases
Presence of a Catalyst
Catalysts are substances that increase the rate of a reaction, by providing an alternative pathway
Catalysts take part in a reaction, but they are unchanged when the reaction is complete So they are present in the reactants and
products and only assist in the rate of the reaction
Temperature
By definition, temperature implies that the greater the temperature, the faster the molecules will move (higher kinetic energy)
When particles are moving faster, more collisions occur and increasing the likelihood of a reaction Higher Temp = particles with more kinetic
energy = more effective collisions
Regents Chemistry
Potential Energy Diagrams
What’s Potential Energy?Chemical bonds are large sources of
chemical potential energy (when bonds are formed)
CHEMICAL ENERGY: energy associated with the breaking and forming of chemical bonds
This is a form of Potential energy!
Chemical Bonds Have PE!
Chemical bonds have large supplies of potential energy
Bonds are broken in chemical reactions and new bonds form in products
Energy can be released or gained in these chemical reactions, so…
Potential energy can be increased or decreased depending on the reaction..
-ENERGY IS ON REACTANT SIDE!
-ENERGY RELEASED: ON PRODUCT SIDE!!!!
What’s a PE Diagram?..First lookA PE diagram illustrates the potential energy
change that occurs during a chemical reaction
---
Pot
enti
al e
nerg
y
Reaction Coordinate
Products
Reactants
Activated ComplexReaction Coordinate = progress of reaction
Potential Energy Diagrams
In order for a reaction to occur, the reactants must have sufficient energy to collide effectively
As reactant particles approach each other, kinetic energy is converted into potential energy
The molecules must also have proper orientation to come together…this leads to..
Activated Complex
When molecules collide with the proper orientation, an intermediate product is formed
Activated Complex – is a temporary, intermediate product that may either break apart and reform the reactants or rearrange the atoms and form new products
Example of Collisions
HI molecules collide in a reaction and form H2 and I2 products
A + B C + D + Heat
Heat is a product because the PE is lower for the products than in the reactants
DifferenceIn PE
Reactants and Products on a PE Diagram
H =Heat of reaction
Activationenergy
Activation Energy and Heat of Reaction
The amount of energy needed to form the activated complex from the reactants is called the activation energy
The diagram is typically read from left to right and vice versa So..we specify by saying forward or reverse
HEAT OF REACTION – is the heat required to form products or reactants in this specific reaction Can be negative or positive depending on viewing the
reaction as forward or reverse
The Effect of a Catalyst
Catalysts are added to a reaction to lower the activation energy, which in turn speeds up the reaction
The catalyst speed up the reaction by providing a new pathway
In turn, the activation energy of the reverse reaction is also lowered…but
The H remains unaffected..see why
Effect of a Catalyst
What does 5 represent?
Two Outcomes of PE Diagrams1. PE of products is lower than the
reactants, so energy is lost and released to the environment – Exothermic! (H = -)
PE of the products is greater than the reactants, so energy is absorbed to make the products – Endothermic (H = +)
Two Outcomes of PE Diagrams