Lecture 3 Rate of Reactions Flashcards
What does rate of reaction (ror) mean?
The speed it takes for different chemical reactions. Some chemical reactions are very fast whereas some are very slow.
What does ror measure?
Ror measures how fast a reactant is consumed or how fast a product is formed. Ror is expressed as a ratio of change in concentration to time taken.
Rate = Change in [A] / Change in t
or Rate = Change in [B] / Change in t
Where Change in [A] and [B] os the change in concentration over a period of time.
What does ror depend on?
Ror depends on anything that increases the number of successful collisions between the reactant particles which will speed up a reaction. Examples are: Increased temperature, increased concentration and pressure, increased surface area and catalysts.
Are what speed do reactions take place?
Reactions do not proceed at a steady rate. They start at a certain speed then get slower and slower until they stop. This is because the concentration decreases over the time with less particles successfully colliding with one another.
How can ror be measured?
Measuring ror means measuring the change in the amount of reactant or the amount of product.
What equipment is required to investigate the rate of hydrogen production?
Conical flask with the hydrochloric acid and reactant (eg magnesium). Rubber bung at the top of the flask attached to a glass tube leading out of the flask with a rubber connector leading to the gas syringe.
What is activation energy?
Activation energy (Ea) is the minimum amount of energy required to initiate a chemical reaction.
What is a catalyst?
A catalyst speeds up the ror by lowering the activation energy. It is not used up in the reaction and does not increase the amount of product, it just increases the speed in which the product is formed.
3 types of catalysts:
Heterogeneous - catalyst and reactant are in different phases
Homogeneous - catalyst and reactant are dispersed in a single phase
Enzyme catalyst- biological catalyst (most essential)
What are some everyday examples of catalysts?
Many catalysts are transition metals or their compounds.
Nickel: Catalyst used in the production of margarine (hydrogenation of vegetable oils)
Iron: catalyst used in the production of ammonia from nitrogen and hydrogen
Platinum: catalyst used in the catalytic converters of car exhausts. It catalyses the conversion of carbon monoxide and nitrogen oxide to less polluting carbon dioxide and nitrogen.
Why are catalysts used in industry?
Product is produced quicker, saving time and money. Also catalysts reduce the need for high temperatures, saving fuel and reducing pollution.
Catalysts are also essential in living things. Biological catalysts are special proteins called enzymes.
What is chemical equilibrium/balance?
At chemical equilibrium, the rates of the forward reaction and reverse reaction are equal and the concentration of the reactants and product remain constant.
k= equilibrium constant aA+bB = (reverse reaction arrows) cC+dD k= [C]c[D]d / [A]a[B]b (product conc / reactant conc)
What factors can affect chemical equilibrium?
Concentration
Pressure
Volume
Temperature
What is Le Chatelier’s Principle
If an external stress is applied to a system at equilibrium, the system will adjust in such a way that the stress is partially offset as it tries to establish a new equilibrium.
What are the affects of changes in concentration to the chemical equilibrium?
When product is added, the system will shift to the reactant side.
When product is removed, the system will shift to the product side.
When reactant is added, the system will shift to the product side.
When reactant is removed, the system will shift to the reactant side.
Simply if reactant is added, concentration has increased on the reactant side so the system will shift towards to product side to reestablish equilibrium.
What are the affects of changes in pressure to the chemical equilibrium?
When pressure is increased, the system shifts to the side with fewer particles to alleviate some of the additional pressure.
