Chapter 9 lesson 3

catalysts speed reactions by helping reactant particles ____ each other more often. a catalyst isn't changed in a reaction, and it doesn't change the ____ or ____. also, catalysts don't increase the amount of reactant used or the amount of product that is made. it only makes a given reaction happen ____. therefore, catalysts ______ considered reactants in a reaction.

contact, reactants, products, faster, aren't

some reactions, such as rusting of iron, have low activation energy. the ____ in the surroundings is enough to ___ these reactions

energy, start

in an ____ reaction, more energy is released when the products form than is required to break the bonds in the reactants. therefore, the overall reaction releases energy.

exothermic

think of a crowded hallway. because the concentration of people is higher in the crowded hallway than in an empty hallway, people probably collide more often. similarly, ____ the concentration of one or more reactants ____ collisions between particles. more collisions result in faster reaction rate. in gases, an increase in ___ pushes gas particles closer together. when particles are closer together, more collisions occur.

increasing, increases, pressure

if a reaction has high activation energy, ___ energy is needed to start the reaction. for example, wood requires the thermal energy of a flame to start burning. once the reaction starts, it _____ enough energy to keep it going

more, releases

preservatives in food are substances that inhibit, or ____ _____, food spoilage

slow down

surface area is the amount of exposed, outer area of a ____. increased surface area _____ reaction rate because more particles on the surface area of a solid come into contact with the particles of another substance. for example, if you place chalk in vinegar, the chalk reacts slowly with the acid. this happens because the acid contacts only the particles on the surface of the chalk. if you grind the chalk into powder, more chalk particles contact the acid, and the reaction occurs faster.

solid, increases

if everyone in a hallway were running, they would probably collide with each other more often and with more energy than if everyone was walking. this is also true when particles move faster. at higher temperatures, the average ____ of particles is greater. this speeds reactions in two ways. one, particles collide more ____. two, collisions with more ____ are more likely to ____ chemical bonds.

speed, often, energy, break

inhibitors

substance that slows, or even stops, a chemical reaction

activation energy

the minimum amount of energy needed to start a chemical reaction

exothermic

a chemical reaction that releases thermal energy

catalyst

a substance that increases reaction rate by lowering the activation energy of a reaction.

breaking a bond ___ energy from the surroundings. the formation of a chemical bond ___ energy to the surroundings.

absorbs, releases.

when a chemical reaction occurs, chemical bonds in the reactants ___ and new chemical bonds ____. chemical bonds contain a form of energy called chemical energy

break, form,

endothermic

chemical reactions that absorb thermal energy

particles must ___ before they react. chemical reactions occur faster if particles collide more ____ or move ____ when they collide.

collide, often, faster

in all chemical reactions, energy is ____

conserved

in an _____ reaction, more energy is required to break the bonds of the reactants than is released when the products form. therefore, the overall reaction absorbs energy

endothermic

some chemical reactions ___ more energy than they ___

release, absorb