Chapter6.2p. 281
Check Your Understanding Answers
Checking Concepts
1. Many possible examples: for example, a highreaction rate helps make explosives useful inhighway construction and demolishing buildings.It also increases the rate at which cookingcan occur. The fast rates of reactions inliving things make it possible for the livingthings to stay alive.
2. Accept all logical answers. For example, refrigerationslows the rate of reactions that cause thedecomposition of foods. Rusting can be limitedby slowing the reactions that produce it. Keeping explosive dusts in an inert atmosphereor keeping them in a compact form reduces theopportunity for a dust explosion to occur.
3. Enzymes are biological catalysts that increasethe rate of chemical reactions in order for anorganism to stay alive.
4. Increasing concentration of a reactant usuallyincreases the rate of a reaction.
5. A spoonful of sugar has greater surface areathan a sugar cube because, in the sugar cube,most of the sugar is on the inside of the material,while in the spoon, the large number ofparticles of sugar have a large surface.
6. Increasing surface area increases the rate of a reaction.
7. For example, when two gases react, there is no surface between them. Hydrogen and oxygengases react to produce water, and surface areais not a factor.
8. A catalyst makes it possible for reactions tooccur with less energy than reactions that donot have a catalyst. The catalyst helps moleculesline up better so that, when they collidewith each other, the reaction takes place withless energy than would otherwise be required.
Understanding Key Ideas
9. (a) Raising the temperature, increasing the concentration
(b) Raising the temperature, adding a catalyst
(c) Raising the temperature increases the number of collisions and also makes themmore effective because the collisions happenwith greater energy.
10. Raising the temperature increases the numberof collisions and also gives the collisions agreater amount of energy.
11. Increasing the surface area gives greateropportunity for reactant particles to collide.This increases the rate of reaction.
12. Increasing the concentration of a reactantgives a greater opportunity for reactant particlesto collide. This increases the rate of areaction.
13. A catalyst helps reactant molecules to line upmore effectively than without a catalyst. Thisallows the reaction to happen with less energy.
Pause and Reflect Answer
Students could cover some of these points.
• Throwing the wrapper back into the original box makes it harder to find wrapped chocolates, so thisslows down the rate of chocolate eating.
• As the reaction proceeds, the reactants become mixed with the products, so the chance of the catalystfinding the reactants decreases, slowing downthe reaction.