Reaction Rates and Equilibrium

Reaction Rates and Equilibrium

Reaction Rates

• Some reactions, such as the combustion of rocket fuel, happens extremely quickly. Other reactions such as rusting take a long time to develop

• Reaction rate is the rate at which reactants change into products

What are some factors that can affect reaction rates?

• The collision model states that atoms, ions, and molecules must collide in order to react

• Understanding the collision model will help to explain why changing the conditions of a chemical reaction can have an effect on the reaction rate

Multiple Choice

When we investigate the rate of reaction we are looking at the...

• amount of product formed

• speed of reaction

• concentration of reacting particles

• combining reactants with products

Factors that affect reaction rate

• Temperature

• concentration

• volume and pressure

• surface area

• catalysts and inhibitors

Temperature

• We often store perishable foods in a refrigerator to keep them from going bad quickly

• remember that temperature is the measure of average kinetic energy so cooling something down will slow the particles and the reaction rate

• Likewise heating a substance will increase the speed and motion of the particles and increase the reaction rate

Multiple Choice

Why does a higher temperature increase the rate of a reaction?

• it increases both the frequency and energy of particle collisions
• it only increases the frequency of particle collisions
• it only increases the energy of particle collisions
• it reduces the activation energy of the reaction

Concentration

• Increasing the concentration of a solution adds more reactant particles which gives more opportunities for collisions to occur

• more collisions = faster reaction rate

volume and pressure

• Volume and pressure are important because they relate to the concentration of reacting gases

• Smaller volume = greater pressure = faster reaction rate

Surface area

• The more surface area that is in contact between the reactants the faster the reaction will occur

• Think about what dissolves quicker...sugar crystals or a sugar cube

Multiple Choice

Which factors increase the rate of a reaction.

• increasing temperature
• increasing concentration
• increasing surface area
• all of these

Multiple Choice

Which of the following increase the reaction rate?

• less surface area
• lower temperature
• an inhibitor
• increased concentration

Multiple Choice

Increase in temperature of the reactants can do one of the following

• Slow collision frequency
• Allow less effective collision between the particles
• Neutralise the reaction
• increase collision between the particles thus increasing the rate.

Multiple Choice

To slow down a chemical reaction you will do one of the following:

• Place the reactants in hot water
• Place the products in ice bath
• Place the reactants in a ice bath
• Keep stirring the reactants with a stirring rod

Catalyst and Inhibitors

• A catalyst speeds up a chemical reaction

• an inhibitor slows down the rate of chemical reactions or prevents them from happening at all

Catalyst

• Catalysts do NOT change the mass of the products they only change how fast they are produced

• Your body uses a special catalyst called enzymes to break down food

Inhibitors

• Inhibitors do NOT change the ammount of product produced, only change the rate at which they are produced

• A common example of an inhibitor would be food preservatives that we add to keep our food from spoiling as quickly as they would otherwise

Equilibrium

• So far the reactions we have looked at have been reactions that "go to completion," meaning they only happen in one direction and continue until all the reactants are consumed/transformed into the products

• There are reversible reactions that can occur in backward and forward directions

• we signify reversible reactions with a double arrow

Equilibrium cont.

• When a reversible reaction's forward and reverse directions happen at the same rate we reach a state of equilibrium or balance

• Equilibrium means our forward and reverse reactions or processes happen at the same rate

Multiple Choice

Define chemical equilibrium.

• A reaction is reversible.
• The concentration of the reactants is equal to the concentration of the products.
• The rate of a forward reaction is equal to the rate of the reverse reaction.
• The reaction stops and no further change in concentration occurs.

Multiple Choice

This symbol indicates that a reaction is ____________

• reversible
• irreversible

Multiple Choice

Some chemical reactions require a substance called a catalyst. The main purpose of a catalyst is

• To warm up the reaction
• To speed up the reaction
• To create more reactants
• To stop the reaction

Multiple Choice

This slows down or even stops a chemical reaction.

• de-activator

• catalyst

• enzyme

• inhibitor

Types of Equilibria

• we can have equilibrium in physical changes as well as chemical changes

Factors Affecting Equilibria

• Just like we have factors that affect reaction rates, there are things we can do to change equilibrium

• Le Chatelier's principle states that if a stress is applied to a system at equilibrium, the equilibrium shifts in the direction that opposes the stress