Rates of Reaction Chemical Change Reaction Chemical reactions

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Rates of Reaction

Rates of Reaction

Chemical Change (Reaction) • Chemical reactions occur when old bonds break and new bonds

Chemical Change (Reaction) • Chemical reactions occur when old bonds break and new bonds form.

Chemical Change (Reaction) • Chemical reactions involve two main kinds of changes that you

Chemical Change (Reaction) • Chemical reactions involve two main kinds of changes that you can observe – – formation of new substances and – changes in energy.

One More Reaction Principle • For a chemical reaction to happen, – There has

One More Reaction Principle • For a chemical reaction to happen, – There has to be enough energy to make it happen. • (Activation Energy) – There has to be a site for it to happen at. • (They have to be close enough to collide – or it’s not going to happen). • Therefore, we can regulate the speed at which a reaction takes place.

Collision Theory • This theory states that reactions will occur only if atoms/ molecules

Collision Theory • This theory states that reactions will occur only if atoms/ molecules within the two (or more) substances collide. • Therefore, if you want to speed up a reaction, you need to collide reactants with more energy or more often. • If you want a reaction to go slower, then you need to keep the reactants from colliding with less energy or less often.

Has to be a site for reactants to meet O H H O H

Has to be a site for reactants to meet O H H O H C H Has to have enough energy to make it happen (Activation Energy) O O Area where bonds break and reform (a chemical reaction)

Release of Energy O H BL O H ! O AM H O C

Release of Energy O H BL O H ! O AM H O C H O Under those conditions, A reaction can take place.

Rates of Chemical Reactions • Ways to speed up or slow down a chemical

Rates of Chemical Reactions • Ways to speed up or slow down a chemical reaction: – Temperature • related to thermal energy – Break it up • increase Surface area. – Concentrations (example: a “stronger” or “weaker” acid) – Stirring/ Agitation – Catalysts and inhibitors.

Adding Heat • When you heat a substance, you make the molecules move faster.

Adding Heat • When you heat a substance, you make the molecules move faster.

Adding Heat • Faster moving particles increase the reaction rate in two ways: –

Adding Heat • Faster moving particles increase the reaction rate in two ways: – The particles come in contact more often. – Faster moving particles have more energy. The arrows are called “vectors”

Adding Heat • This increased energy causes more particles of the reactants to get

Adding Heat • This increased energy causes more particles of the reactants to get over the activation energy “hump”. Demo: Match contents and oxygen Demo: Anything that catches fire – i. e. Bunsen burner. Demo: Food dye in Hot v. Cold Water

Increased Surface Area • By breaking a substance into smaller pieces, more particles are

Increased Surface Area • By breaking a substance into smaller pieces, more particles are exposed and the reaction happens faster. Demo: Whoosh Bottle v. burning on table. Demo: Cutting a cube of clay

Increased Surface Area • More surface area=more space for atomic collisions reactions

Increased Surface Area • More surface area=more space for atomic collisions reactions

Concentration Levels • Concentration: The amount of a substance in a given volume. –

Concentration Levels • Concentration: The amount of a substance in a given volume. – Ratio of Reactants to Inactive ingredients • Increasing the concentration of reactants supplies more particles to react. Demo: Vinegar v. Diluted Vinegar & Baking Soda

Has to be a site for reactants to meet O O H H O

Has to be a site for reactants to meet O O H H O O H C O O H Has to have enough energy to make it happen (Activation Energy) O O Area where bonds break and reform (a chemical reaction)

Release of Energy O O O H O BL O H ! O AM

Release of Energy O O O H O BL O H ! O AM H O O O C H O O Under those conditions, A reaction can take place.

Has to be a site for reactants to meet O O N N H

Has to be a site for reactants to meet O O N N H H N N N H C N H Has to have enough energy to make it happen (Activation Energy) N O O N Area where bonds break and reform (a chemical reaction) Under these conditions, a limited (less explosive) chemical reaction takes place

Stirring, Shaking, Agitation • By stirring, you make the molecules come close enough more

Stirring, Shaking, Agitation • By stirring, you make the molecules come close enough more often which allows the particles to come in contact more often. – This mainly applies only for physical changes more so than chemical reactions. • i. e. Salt & Water

Catalyst • Material that increases the rate of a reaction by lowering the activation

Catalyst • Material that increases the rate of a reaction by lowering the activation energy. • Provide a surface on which reactions can take place. • They are not affected by the reaction. • Example: Enzymes in the body. Demo: burning a potato chip – v. body burning it.

Inhibitors • Inhibitors react with the substances first before the reactants do. • So,

Inhibitors • Inhibitors react with the substances first before the reactants do. • So, they slow down the reaction • When would you want to use an inhibitor? • Example: Fireworks