Unit 6 Kinetics and Equilbruim

For a collision to be successful it must have:

A sufficient amount of energy when the collision takes place. The reacting particles must be in the proper orientation so that bonds can be broken and new bonds made.

What is a catalyst, and what do they change about a chemical reaction?

A catalyst is a chemical that speeds up a reaction without being used up in the reaction itself. It does this by lowering the activation energy of the specific reaction which makes it easier for a collision to be successful.

Change in Pressure/Volume (Gases)

A change in pressure is comparable to a change in volume. If the volume decreases the pressure increases. If the volume increases the pressure decreases. An increase in pressure (decrease in volume) always favors the reaction that produces fewer molecules of gas in the system. A decrease in pressure (increase in volume) favors the reaction that produces more molecules of gas in the system. After the pressure is changed equilibrium will be reestablished at a new equilibrium point.

activation energy

Activation energy is the minimum amount of energy that reactants must have when they collide in order to produce a successful collision. Each reaction has a specific activation energy.

Factors that Effect Rate

Agitation Concentration Temperature Surface Area (Particle Size) Catalyst

Change in Concentration

An increase in concentration of either the reactant(s) or product(s) will favor the reaction that uses the substance added.

Change in Temperature

An increase in temperature will always favor the endothermic reaction. A decrease in temperature favors the exothermic reaction. Exothermic Reaction- Chemical reaction where heat is released A + B ⇄ C + D + Heat. Endothermic Reaction- Chemical reaction where heat is absorbed A + B + Heat ⇄ C + D.

WHAT IS REACTION KINETICS?

It is the study of the factors that can influence the RATE or SPEED of a reaction. Rate describes how fast a reactant is used or how fast a product is formed in a reaction under a specified set of conditions (temperature, pressure, etc).

Catalysts

Catalysts work in several ways to lower the activation energy 1. They can provide a surface for the reaction (putting H2O2 on a cut, the blood cells provide a surface for the decomposition of the H2O2) 2. They can provide proper orientation for a successful collision (enzymes frequently act this way) 3. They can stretch bonds and make them easier to break (Au used to weaken bonds between N & O in N2O) 4. They can form an unstable intermediate (decomposition of H2O2 by NaI(aq)) In each case mentioned above, they lower the activation energy needed for the reaction to take place.

static equilibrium

Children on a see-saw. At the balance point (the equilibrium position), there is no movement of the children or the seesaw (the opposing processes)

Factors that affect a system in equilibrium

Concentration Temperature Pressure/Volume (gases) The underlying rule is referred to as LeChatlier's Principle

How does equilibrium relate to chemical reactions?

Equilibrium occurs in a chemical reaction when the rates of the forward and reverse reaction are equal. This means that as the reactants are turning into the products the products are forming back into the reactants at the same time. This means that the concentration (amount) of reactants and products is constant even though the reactions are still taking place.

According to the collision theory what state of matter is most favorable to have successful collisions? Why?

Gases tend to react faster than solids or liquids. It takes energy to separate particles from each other. Aqueous ions tend to react faster than species in other states of matter because the ions are already separated from each other.

LeChatlier's Principle

LeChatlier's Principle uses the idea that a system will always try to reach equilibrium. If a stress, such as concentration change, temperature change, or pressure change (or volume change in systems involving gases) is placed on the system, the system will temporarily favor the forward or the reverse reaction until equilibrium is re-established.

Dynamic Equilibrium

In most systems, there are two reactions occurring, the forward reaction and the reverse reaction. When the rate of the forward reaction and the reverse reaction are equal we say the system is in equilibrium (at a specified set of conditions). At equilibrium the concentrations of both reactants and products stay constant. (Child moving up an escaltor at a constant rate.)

Are all chemical collisions successful? Why or why not?

Not all collisions are successful. Reactants need to collide with enough energy and in the correct orientation to be successful.

Surface area.

Surface area refers to the amount of space exposed for collisions between reactants. The greater the size of the sample the smaller the surface area. The smaller we make the particle size the greater the surface area. Since reactions require collisions-the more places that collisions could have the more successful collisions are possible.

How does the collision theory explain how chemical reactions occur?

The collision theory explains that for a reaction to happen that the reactants must collide and interact with one another. Not all collisions are successful though, for a reaction to take place each collision must have both, a minimum amount of energy and the proper orientation.

What is collision theory and how does it affect chemical reactions?

The collision theory states that when suitable particles of the reactant hit each other, only a certain percentage of the collisions cause any noticeable or significant chemical change; these successful changes are called successful collisions. The successful collisions have enough energy, also known as activation energy, at the moment of impact to break the preexisting bonds and form all new bonds. This results in the products of the reaction.

Characteristics of Dynamic Equilibrium

The concentrations of the reactants and products (macroscopic properties) remain the same but the reactions don't stop! The reactants are still reacting to form the product and the product is still being converted back to the reactants (microscopic processes).

Explain the difference between dynamic and static equilibrium. Use an example of your own to illustrate your explanation.

The difference between dynamic and static equilibrium is what is happening inside the chemical reaction. If something is to be at dynamic equilibrium, it would be changing at a constant rate. This means that my reactants and products are changing in a way that the amounts I have of each remain constant. If the reaction is at static equilibrium, it means that there is nothing is moving. The reactants and products will remain at a constant concentration because no reaction is taking place.

Why does changing the temperature of the reaction affect the rate of a chemical reaction?

The higher the temperature, the faster the particles are moving. The faster the particles are moving, the greater the chances for collisions. The faster the particles are moving, the more energy they will have at the time of collision. The more energy at the time of collision and the greater chance for collisions, the more successful collisions in a given amount of time. The more successful collisions in a given amount of time, the faster the rate of the reaction.

Why does changing the concentration of chemicals change the rate of a chemical reaction?

The more particles in a reaction the more chances it has of a successful collision in a given amount of time therefore causing a faster rate.

Equilibrium and Rate

The rate at which the reactants change into products is exactly equal to the rate at which the products change back to the original reactants. Thus it appears as if the reaction has stopped, but in actual fact, it is still going on.

When Adding reactants or products

The shift goes away from the addition because it needs to use up the extra reactant/product

When Removing reactants or products

The shift goes toward the reduction because it needs to replace the reactants/products removed.

What is the rate of a reaction? Why is it important in chemistry?

The speed at which reactants are converted into products in a chemical reaction. This is very important because it helps indicate the way that chemicals react and also helps chemists create chemicals on an industrial scale.

Equilibrium

To indicate a system has reached equilibrium, double arrows are frequently used. There are two types of systems to be studied - - Dynamic Equilibrium - Static Equilibrium

How do we know which side is favored?

To indicate the reaction that is favored as a result of a stress we will use double arrows of unequal length. In this case, we are indicating that the forward reaction is favored (or there is a shift to the right), if a reverse reaction is favored then the arrow shifts left. Shift AWAY from addition, Shift Toward Reduction. Changing concentrations of SOLIDS and PURE LIQUIDS doesn't cause a shift in equilibrium! Only concerned with aqueous (aq) and gaseous (g) substances!

What is a reversible reaction?

a chemical reaction in which the products can be converted back to reactants under suitable conditions. The reaction involves two reactions. There is a "forward" reaction and a mirror image "reverse" reaction. A reversible reaction is shown by the sign a half-arrow to the right (forward reaction) and a half-arrow to the left (reverse reaction).

Temperature

a measure of average Kinetic Energy. Since reactions collisions require energy -the greater the temperature, the faster the particles are moving. All reactions require certain minimum activation energy to get them started.

Concentration

is the abundance of a constituent divided by the total volume of a mixture. Since reactions require collisions - the greater the number of reacting particles the greater the chances for successful collisions. The greater the concentration the faster the rate of reaction (more collisions -> more successful collisions.)

As Temperature increases As Temperature decreases

it shifts to use up the extra energy it shifts to replace the energy lost

As Pressure increases As Pressure decreases (Only for gas molecules)

they shift towards the side with fewer gas molecules. they shift towards the side with more gas molecules. If the number of gas molecules are equal then no change occurs.