Reaction Rates and Equilibrium

temporary, unstable structure formed when reacting particles collide

Activated Complex

energy required to start reaction

Activation Energy

Increasing the temperature of a chemical reaction causes the equilibrium position of a reaction to shift in the direction that absorbs the heat. Always true sometimes true never true

Always true

what is stress in relation to equilibrium?

An applied force or system of forces that tends to shift a reaction.

A catalyst is considered a reactant in a chemical reaction. True False

F

If the activation energy is low (small hill), then chances are good that many particles will collide with enough energy. This translates to a FAST ___ reaction.

FAST

If volume decreases (there is less space), pressure increases, and the equilibrium will shift to the side with ____ gases.

FEWER

Why would gases react faster?

Gases react faster because their particles are moving around the fastest and are able to collide with other reactant particles more often.

What does the value (the number) of Keq tell you?

If Keq > 1 the forward reaction is favored If Keq =1 neither is favored If Keq< 1 the reverse reaction is favored

Use the collision theory to explain why a mixture of hydrogen gas and chlorine gas reacts faster when the volume they occupy is decreased.

If the volume is decreased, the gas molecules are closer together and have a greater chance of making effective collisions.

What is the collision theory

In order for particles to react with each other, they must collide

Why would iron filings rust faster than an iron nail?

Iron filings have a greater surface area than the nail. This exposes a greater area of contact between the reactants.

Write equilibrium constant expressions S03(g) + H20(1) <==> H2SO4(1)

Keq= 1/ [SO3]

Write equilibrium constant expressions for the following equilibria NH4C1(s)<--> NH3(g) + HCI(g)

Keq= [NH3] [HCl]

For the equilibrium system PCl5equation image indicator PCl3 + Cl2, Keq = 35. If the concentrations of PCl5 and PCl3 are 0.025M and 0.68M respectively, what is the concentration of the Cl2?

Keq= [PCl3] [Cl2]/[PCl5] 35= [.68] [Cl2]/[.25] [Cl2]= 1.3M

For the reaction, 2SO3<-->2SO2 + O2, [SO3]=0.37M, [SO2]=0.25M, [O2]=0.86M. Write the Keq equation, calculate Keq, and explain what this value means.

Keq= [SO2]^2 [02]/[SO3]^3 Keq= [.25]^2 [.86]/[.37]^3 Keq= .39 Since Keq <1 it favors the reverse reaction

If product is added, it will shift ___

LEFT

When you add a product to a reversible chemical reaction, the reaction always shifts _______ . When you remove a product, the reaction shifts ____.

Left right

What are the TWO characteristics of an effective collision?

Particles must collide with the correct orientation and the proper amount of energy.

Based on your knowledge of factors affecting the rate of reaction, why is there a danger of explosions in places such as silos and coal mines where there are large quantities of powdered, combustible materials?

Powdered materials have a higher surface area than solid materials. When large quantities of powdered, combustible materials are present, the chances of an effective collision are increased.

If reactant is added, the equation will shift ___

Right

On a potential energy diagram, if the activation energy is high (tall hill), then there will not be very many particles that collide with enough energy. T/F

T

When a reaction is at equilibrium, what two things are equal?

The rates of the forward and reverse reactions

The way to increase the rate of a reaction is to increase the number of effective collisions True False

True

Due to decomposition reactions with oxygen or carbon dioxide in the air, meat begins to feel slimy and smell spoiled. Explain, using your knowledge of chemical kinetics, why meat spoils less rapidly when left unsliced.

Unsliced meat would have a lower surface area. This means that fewer particles are exposed to the oxygen or carbon dioxide in the air, slowing the spoiling.

Why would a mixture of gases react faster when the volume they occupy is decreased?

When the volume of the gases is decreased, the particles are forced closer together. This increases the chances of an effective collision.

In the reaction 2NO (g) + H2 (g) <--> N2O (g) + H2O (g) + heat, will the [H2O] increase or decrease when equilibrium is reestablished after N2O is removed? a. increase b. decrease

a. increase

In the reaction 2NO (g) + H2 (g) <--> N2O (g) + H2O (g) + heat, will the [H2O] increase or decrease when equilibrium is reestablished after NO is added? a. increase b. decrease

a. increase

In the reaction N2 (g) + 3 H2 (g) <--> 2NH3 (g) + 22 kJ, will the [H2] increase or decrease when equilibrium is reestablished after NH3 is added? a. increase b. decrease

a. increase

Which of the following will NOT speed up a chemical reaction? a. increasing the concentration b. adding a catalyst c. decreasing the temperature d. increasing the surface area

a. increasing the concentration

In the reaction 2NO (g) + H2 (g) <--->N2O (g) + H2O (g) + 36 kJ, in which direction will the equilibrium shift if N2O is added? a. left b. right

a. left

In the reaction 2NO (g) + H2 (g) <--> N2O (g) + H2O (g) + 36 kJ, in which direction will the equilibrium shift if H2 is removed? a. left b. right

a. left

In the reaction CO2 (g) + H2 (g) + heat <--->CO (g) + H2O (g), in which direction will the equilibrium shift if CO is added? a. left b. right

a. left

In the reaction CO2 (g) + H2 (g) + heat <--->CO (g) + H2O (g), in which direction will the equilibrium shift if H2 is removed? a. left b. right

a. left

What is the effect of a catalyst on the required energy to achieve effective collisions? a. A catalyst increases the required energy (activation energy) for a reaction to take place. b. A catalyst lowers the required energy (activation energy) for a reaction to take place. c. A catalyst does not affect the required energy (activation energy) for a reaction to take place.

b. A catalyst lowers the required energy (activation energy) for a reaction to take place.

How does decreasing temperature affect the rate of reaction. a. Decreasing tempearture increases the rate of reaction. b. Decreasing tempearture decreases the rate of reaction. c. Decreasing tempearture does nothing to the rate of reaction.

b. Decreasing tempearture decreases the rate of reaction.

Reaction rate measures the speed at which reactants: a. appear b. disappear

b. disappear

2 NO (g) + H2 (g) <--> N2 (g) + H2O (g) + energy In which direction will the equilibrium shift if the temperature is decreased? a. left b. right

b. right

In the reaction 2NO (g) + H2 (g) <---> N2O (g) + H2O (g) + 36 kJ, in which direction will the equilibrium shift if NO is added? a. left b. right

b. right

In the reaction 2NO (g) + H2 (g) <---> N2O (g) + H2O (g) + 36 kJ, in which direction will the equilibrium shift if the pressure is increased? a. left b. right

b. right

In the reaction CO2 (g) + H2 (g) + heat <--> CO (g) + H2O (g), in which direction will the equilibrium shift if temperature is increased? a. left b. right

b. right

How do catalyst work?

by lowering the activation energy (Ea)

Enzymes are in molds and bacteria that spoil food. Why doesn't food spoil as fast when it is refrigerated as it would at room temperature? a. Food that is at room temperature has slower moving particles than food that is refrigerated. This increases the chance of an effective collision. b. Food that is at room temperature has faster moving particles than food that is refrigerated. This decreases the chance of an effective collision. c. Food that is at room temperature has faster moving particles than food that is refrigerated. This increases the chance of an effective collision.

c. Food that is at room temperature has faster moving particles than food that is refrigerated. This increases the chance of an effective collision.

In order for a collision to be considered effective, the reactant particles must have the correct orientation and the proper amount of: a. space b. concentration c. energy d. surface area

c. energy

When equilibrium is reached, the concentration of products a. increases. b. decreases. c. remains the same.

c. remains the same.

When equilibrium is reached, the concentration of reactants a. increases. b. decreases. c. remains the same.

c. remains the same.

List examples of catalysts

catalytic converter enzymes in the body

Magnesium metal will react more quickly in 6 M hydrochloric acid than in 1 M hydrochloric acid due to the increased _____.

concentration

The concentration of reactants and products in a system at dynamic equilibrium are ___________

constant

How can you indicate in a chemical equation that a reaction is reversible?

double arrows

characterized by or causing the absorption of heat

endothermic

substance that acts as a catalyst in the body

enzyme

List 3 applications of inhibitors

food preservatives weed killers medicine

Would you expect solids, liquids, or gases to react faster?

gases

in potential energy diagram high hill = ______ small hill= ______

high= slow reaction small= fast

What are the 2 types of equilibrium

homogeneous heterogenous

What will happen to reaction rate with increased temperature

increase

one that inhibits as a substance that retards or stops a chemical reactoin

inhibitor

What is a catalyst

is a substance that is added to a reaction to make it go faster

Salt will dissolve more quickly in 70°C water than in 20°C water due to the water molecules' increased _____.

kinetic energy

the study of the rate of reactions

kinetics

In the reaction CO2 (g) + H2 (g) + heat <-->CO (g) + H2O (g), in which direction will the equilibrium shift if H2 is removed? a. left b. right

left

List The five factors that affect reaction rates

nature of the reactants, concentration of the reactants, temperature, presence of any catalysts, surface area.

Chemical equilibrium is a state in which the forward and reverse reactions take place at different rates Always true sometimes true never true

never true

Are catalysts used up in the reaction?

no, they can be used over and over again.

Will 2 solids react with each other?

rarely

the change in reactant concentration per change in time

reaction rate

Double arrows in an equation mean that the equation is

reversible

can occur in measurable amounts in either direction.

reversible reaction

If reactant is removed, it will shift ___

shift Left

In heterogeneous reactions what type of substances don't appear in the equilibrium constant expression?

solids and liquids.

a change in the pressure on a system can cause a shift in the equilibrium position. Always true sometimes true never true

sometimes if there is a difference in # gases

When a substance is ground into a fine powder, it will react faster due to an increase in _____.

surface area

What is equal in a state of equilibrium?

the rates of the forward and reverse reactions

How does increasing the concentration of reactants speed up a reaction rate?

there are more reactants to collide with

____ state- synonym for activated complex

transition

What does the Le Châtelier's Principle state

when a reaction is at equilibrium and a stress is added (change in temperature, concentration, or pressure), the reaction will shift to reduce that stress.

When is a reaction said to be in equilibrium?

when the rates of the forward and reverse reactions are equal.

If you increase the temperature, the equilibrium will shift to the side____

with heat.

If you increase the temperature, the equilibrium will shift to the side _______

without heat.