Chapter 16 Flashcards
Explain what is meant by the average rate of reaction
It is the overall difference in concentration divided by the amount of time that has passed. It is an average because instantaneous reaction rates vary, but you’re considering the rate over an extended time period.
What happens to the concentration of reaction of the reactants and products during the course of a chemical reaction?
During the course of the reaction the concentration of the reactants goes down and the concentration of the products goes up.
How would you express the the rate of chemical reaction A - B based on the concentration of reactant A? How would the rate compare with the reaction rate based on product B?
It think the point of this problem is to acknowledge that reaction rates are always positive, so if it is being expressed in terms of A you would need to multiply by negative 1 when you subtract the initial concentration from the final (In a reaction the concentration of a the reactant will always go down, so if you subtract the initial from the final it will always be negative…). If you express the rate interms of B (the product) you don’t need to multiply by negative 1 because it will already be positive. JUST REMEMBER THAT REACTION RATES SHOULD ALWAYS BE POSITIVE.
What is the role of an activated complex in a chemical reaction
The activated complex is a transition where all the reactants are temporarily together. This allows the “old” bonds to break and the “new” bonds to form.
Suppose two molecules that can react collide. Under what circumstances do the colliding molecules not react?
They do NOT react if they collide in the incorrect orientation, and they do NOT react if they don’t have sufficient energy to form the activated complex (or overcome the activation energy)
Apply the collision theory to explain why increasing concentration of the reactant usually increases the reaction rate?
An increase in reactant concentration usually results in an increase in reaction rate.
Explain why a crushed solid reacts with a gas more than a large chunk of the same solid?
An increase in reactant concentration usually increases the reaction rate because there are more reactant particles in the reaction vessel. If there are more particles they are more likely to collide, or will collide more frequently. The particles have to collide in order to react.
Apply the collision theory to explain why food usually spoils more slowly when refrigerated
Food “spoiling” is a chemical reaction. A decrease in temperature usually causes a decrease in reaction rate because the kinetic energy of the reacting (spoiling) molecules decreases, so when they collide they don’t have enough energy to overcome the activation energy to react.
Hydrogen peroxide decomposes to water and oxygen gas more rapidly when manganese dioxide is added. The manganese dioxide is not consumed in the reaction. Explain the role of the manganese dioxide.
Manganese dioxide must be a catalyst. It works to decrease the activation energy and speed up the reaction (usually by helping the reactants orient themselves correctly in the collision)
Distinguish between a simple and a complex reaction, anelementary step, and a reaction mechanism.
A simple reaction only has one step, a complex reaction has more than one step. Each step is referred to as an elementary step. A list of all of the steps considered as a whole is referred to as the reaction mechanism.
Concentration
Reaction speeds up when concentration of reacting particles increase
Tempature
Temperature increase the reaction rate
Catalysts
A substance that increases the rate of reaction by lowering the activation energies, but is not consumed in the reaction
Inhibitor
Slows down the reaction
Homogeneous catalyst
A catalyst the exists in the same physical state as the reaction it catalyzes
