Ch.14 - Rates Of Reaction Flashcards
What is the rate of reaction?
The rate of reaction is the change in concentration per unit time of any one reactant or product.
What is the instantaneous rate of reaction?
The instantaneous rate of reaction is the rate of reaction at a particular point in time during the reaction.
What are factors that affect the rate of reaction?
Concentration of reactants, temperature of reaction, particle size of solid reactants, nature of reactants and presence of a catalyst.
How does concentration of reactants affect the rate of reaction?
An increase in the concentration of the reactants usually increases the rate of the reaction. Increased concentration means that there are a greater number of reactant particles per unit volume. As a result, the number of collisions per second increases, increasing the rate of reaction.
How does temperature affect the rate of reaction?
An increase in temperature usually brings about an increase in the reaction rate. The average kinetic energy of molecules is proportional to the temperature. So, the higher the temperature, the greater the kinetic energy. This has 2 consequences: The number of collisions per second is increased and the number of effective collisions(collisions with activation energy) is increased.
How does the particle size affect the rate of reaction?
In reactions where one reactant is liquid and the other solid, the more finely divided the solid, the faster the reaction. This is because the solid then has a greater surface area for reaction.
What is a catalyst? How do they work? What group of elements are they typically?
A catalyst is a substance that alters the rate of a chemical reaction but is chemically unchanged at the end of the reaction. They work by lowering the activation energy, They are often transition metals.
What is heterogeneous catalysis?
Heterogeneous catalysis occurs when the catalyst is in a different phase(state) to the reactant. i.e. solid and liquid. It is seen when manganese oxide catalyses the decomposition of hydrogen peroxide and oxygen and water. It is also seen in the dehydration of ethanol to form ethene with aluminum oxide as the catalyst.
What is homogeneous catalysis?
Homogeneous catalysis occurs when the catalyst is in the same phase as the reactants.
What is autocatalysis?
Autocatalysis occurs when a product of a reaction increases the rate of reaction (acts as a catalyst). It is seen in the reduction of manganate ions. With autocatalysis, the initial rate of reaction is slow, but increases once the catalyst is formed. The Manganese(2+) ions are produced and catalyse the reaction. The first few drops of MnO4- added to the Fe2+ solution react slowly while subsequent drops react rapidly.
What pollutants do car engines emit?
Amongst the pollutants are carbon monoxide, nitrogen monoxide, nitrogen dioxide and unburned hydrocarbons.
What are catalytic converters? How do they use catalysts?
Catalytic converters reduce the amount of harmful gases released from a car’s engine. The catalyst is a mixture of transition metals, platinum, rhodium and palladium in the form of a powder. The catalyst is spread in a very thin layer over a ceramic support material full of tiny holes that provide a large surface area.
What are the harmful gases emitted by car engines converted to?
Carbon monoxide reacts with oxygen to produce carbon dioxide. Carbon monoxide reacts with nitrogen monoxide to produce carbon dioxide and nitrogen. Unburned hydrocarbons react with oxygen to produce CO2 and water (octane).
What is activation energy?
Activation energy is the minimum energy with which particles need to collide to cause a reaction.
What is the intermediate formation theory of catalysis?
Sometimes, with homogeneous catalysts, they work by reacting with reactants to form unstable intermediate products. These intermediates decompose readily forming products and regenerating the catalyst. (This is seen in the use of aqueous cobalt chloride in reaction with hydrogen peroxide and an aqueous solution of potassium sodium tartrate.)
