Why is the reaction rate for reactants defined as the negative  of the change in reactant concentration with respect to time, whereas for products it is defined as the change in reactant concentration with respect to time (with a positive sign)?

A reaction is started by mixing reactants. As time passes, the rate decreases. Explain this behavior that is characteristic of most reactions.

Explain what is meant by the average rate of a reaction.

Rate law experiments dont always give data in the form of a rate in moles per second. Some of them give an amount of time necessary for a reaction to proceed to a given point. The faster the rate, the less time necessary. For the following data, assume that the time given is to react 0.10M of A. Determining the complete rate law for the reaction A+Bproducts. Time taken (s) [A] [B] 36.8 0.20 0.40 25.0 0.20 0.60 10.0 0.50 0.60 A classic chemical reaction/demonstration called the iodine clock reaction is usually measured this way.

Substances that poison a catalyst pose a major concern for many engineering designs, including those for catalytic converters. One design option is to add materials that react with potential poisons before they reach the catalyst. Among the commonly encountered catalyst poisons are silicon and phosphorus, which typically form phosphate or silicate ions in the oxidizing environment of an engine. Group 2 elements are added to the catalyst to react with these contaminants before they reach the working portion of the catalytic converter. If estimates show that a catalytic converter will be exposed to 625 g of silicon during its lifetime, what mass of beryllium would need to be included in the design?

What is the role of the activated complex in a chemical reaction?

a What happens to a reaction rate as temperature drops? Give two explanations for the change. State which one is more important and explain why. b How does a catalyst affect reaction rates? c Compare reaction rates when a given reactant concentration is high with the rate when the concentration is low. Explain the difference.

How do chemists envision reactions taking place in terms of the collision model for reactions? Give an example of a simple reaction and how you might envision the reaction’s taking place by means of a collision between the molecules.

For each of the following pairs of reaction diagrams, identify which of the pair is catalyzed:

Apply collision theory to explain why powdered zinc reacts to form hydrogen gas faster than large pieces of zinc when both are placed in hydrochloric acid solution.