Ch 17 Review Answers 1-4

1. According to the collision model, what determines whether colliding molecules will

    break bonds and form new products?

     Two substances must collide with sufficient energy to break bonds and allow new bonds to form.

2. Higher concentrations of reactants and higher temperatures increase the rate of formation of products. 

    How does the collision model explain these observations? ‘Increase the rate” means the reaction proceeds faster.

1. higher concentrations – Higher concentrations lead to more collisions and therefore to more reaction events.
2. Tigher temperatures – The speeds of the molecules increase with temperature. So at higher temperatures, the average collision is more energetic.

3. Sketch a graph of the progress of a chemical reaction showing the activation energy,  E_a, for the

    reaction.  Explain the graph for the decomposition of BrNO into NO and Br₂.

   

See p 539 Figure 17.3 If the energy contained in a collision of two BrNO molecules is greater than E_a, the colliding molecules bounce apart unchanged.

4. How does a catalyst increase the rate of a reaction?  Sketch a graph showing the effect of the catalyst

    on the E_a of the reaction.    See p 539 Figure 17.4

A catalyst provides a new pathway for the reaction with a lower activation energy than the original pathway, because more collisions will have enough energy to allow a reaction. This in turn leads to a faster reaction.