CHAPTER 7 Chemical reactions form new substances by breaking and making chemical bonds.

Section 7.1 students will: Recognize evidence of a chemical change Identify five types of chemical reactions Describe how the rate of a chemical reaction can change

chemical reactions occur everyday Our food digests Metal left outside rusts Log in the fireplace burns and turns to ash Remember we talked about some changes are PHYSICAL while some are CHEMICAL. A physical change is simply a change in the state of matter while a chemical change involves breaking existing bonds and new bonds forming. Give an example of a physical change: ice melting (any change of state) Give an example of a chemical change: fuel cell car, match burning, milk souring, digestion

Reactants–bonds broken Products–new bonds formed A chemical reaction produces new substances by breaking bonds are rearranging atoms (required energy) Reactants-substances present at the beginning of a chemical reaction. Products-substances formed by the chemical reaction. Reactants–bonds broken oxygen (O2) (CH4) methane + Products–new bonds formed carbon dioxide (CO2) (H2O) water

• Chemical changes occur through chemical reactions. • Evidence of a chemical reaction includes a (1) color change, the (2)formation of a precipitate (solid), the (3)formation of a gas, and a (4) change in temperature.

Types of chemical reactions Synthesis- two or more substances combine to form a new compound Easy way to think of synthesis A + B → C gives +

Decomposition – a reactant breaks down into simpler products Decomposition – a reactant breaks down into simpler products. One large thing breaks down into smaller parts. Simple way: C → A + B Hydrogen peroxide breaks down into hydrogen gas and oxygen gas if not stored in a closed brown bottle. 2H2O2→ 2H2O + O2 Elephant Toothpaste

Single replacement reaction- a single element and a compound produces a new single element and a new compound. Easy way: A + BC → AB + C

An iron nail in copper sulfate produces copper and iron sulfate. Single replacement reaction

Double replacement reaction: Compounds switch “partners” Simple way: AB + CD → AC + BD Just think of it as square dancing in PE. Two couples dosi doeing and the teacher says switch partners. Two compounds (reactants) and when the reaction takes place the products are two new compounds.

Burning methane is a combustion reaction. In a combustion reaction, one reactant is always oxygen and another reactant often contains carbon and hydrogen. Burning methane is a combustion reaction.

Rates of chemical reactions can vary 1. Increasing the concentration of reactants means that there are a larger number of particles that can collided & react. Concentration ~ a high concentration of reactants means there are a larger number of particles that can collide and react. What happens when you turn up the valve on a gas camp stove? More gas molecules to combine with oxygen and a bigger flame.

When do you expect to most likely bump into another shopper at the mall The day after Thanksgiving? Or At 9 PM on a cold Tuesday night in mid January ? Of course Black Friday! A greater concentration of people increases the chance you’ll bump into another person.

2. Increasing the surface area helps create a faster chemical reaction. Which would burn faster? A huge log on my fireplace or that big log ground into saw dust and blown across the fire? The saw dust Which dissolves faster a crushed alka seltzer or a whole one? The crushed one

The rate of a reaction may be increased by making the particles move faster. 3. Increasing the temperature increases the movement of molecules. When does the sugar dissolve in tea better? Hot or cold Does an alka seltzer dissolve faster in hot water or cold water? Does a light stick glow brighter in a cup of hot water or cold water?

4. Adding a catalyst speeds up the rate of a chemical reaction but the catalyst remains unchanged. EX) Enzymes in our bodies help reactions take place. Without them we couldn’t live. Our food would not digest. -Catalysts lower the activation energy of a reaction Catalytic converters on our cars make fuel use more efficient and release less emissions.

Identifying Reactions 2 CO + O2  2 CO2 4 Fe + 3O2  2 Fe2O3 2 H2O2 2 H2O + O2 2 KBr + Cl2  2 KCl + Br2 C6H6 + Cl2  C6H5Cl +HCl ZnCl2  Zn + Cl2 4 H2 + Fe3O4  3 Fe + 4H2O AgNO3 + NaCl  AgCl + NaNO3 Mg + 2 HCl  MgCl2 + H2 Ca(OH)2 + 2 HNO3  Ca(NO3)2 + 2H2O S D SR SR D SR DR SR DR

7.1 Section 7.1 outline I. Chemical reactions alter arrangements of atoms. A. Atoms interact in chemical reactions. 1. Physical Changes 2. Chemical Changes 3. Reactants and Products 4. Evidence of Chemical Reactions B. Chemical reactions can be classified. C. The rates of chemical reactions can vary. 1. Concentration 2. Surface Area 3. Temperature 4. Catalysts

How are physical changes different from chemical changes? review How are physical changes different from chemical changes? What are the 4 evidences of a chemical reaction? How can the rate of a chemical reaction be changed? How might chewing your food be related to the rate of a chemical reaction? Name the 5 types of chemical reactions.

Chapter 7 Section 2 Objectives: Learn why total mass does not change in a chemical reaction. Recognize how a chemical equation represents a chemical reaction. Learn how to balance chemical equations.

The law of conservation of mass states that in a chemical reaction the masses of the reactants and products are equal. Atoms are never gained or lost during a chemical reaction

That means that in a reaction what you have in the beginning of a reaction you have all of the same stuff in the end it has often just changed phases. In other words mass is neither created or destroyed, it just changes form.

Careful observations by Lavoisier led to the discovery of the conservation of mass.

Chemical reactions can be described by chemical equations. CH4 + O2 → CO2 + H2O Reactants yields products

Chemical equations must be balanced. http://www.schooltube.com/video/db41eba5cdbd45fcbe75/ http://www.youtube.com/watch?v=QjVYz00-Kxc&safety_mode=true&persist_safety_mode=1&safe=active

Why do you need to balance equations? All atoms must be equal on the reactant and product sides. Law of Conservation of Mass

Count the Number of Atoms: CH4 + O2 CO2 + H2O C C H H O O 1 4 2 1 2 3

Using Coefficients A Coefficient is a number that indicates how many molecules take part in the reaction A coefficient is written in front of the molecule formula. A subscript is written below element symbols within a molecule formula. You CAN NOT change the subscripts!

Using Coefficients to Balance CH4 + O2 CO2 + H2O C C H H O O 2 2 1 4 1 4

Balanced Review State the law of conversation of mass Is the following equation balanced? CO → C + O2 A chemical equation must be? Mass can not be created or lost 2 2 Balanced

Chapter 7 Sections 3 & 4 Objectives: Describe how energy changes in a chemical reaction. Explain how some chemical reactions release and some absorb energy. Identify the relationship between the reactions of respiration and photosynthesis. Recognize how chemistry has been used to develop technology. Infer through an experiment how catalysts affect a chemical reaction.

Chemical reactions involve energy changes. Chemical reactions involve breaking bonds in reactants and forming new bonds in the products. The energy associated with bonds is called bond energy. Energy is needed to break bonds. Energy is released when bonds are formed.

A reaction where energy is released is an exothermic reaction. Theses reactions typically experience an increase in temperature Changing from a liquid to a solid releases energy----this is an exothermic process. Energy can be released as light or heat.

Other examples of exothermic reactions Combustion of methane is an exothermic reaction. Example-- the house explosion in Florence. A glow stick works by a chemical reaction that releases light. Lightening bugs light up due to a chemical reaction as do some fish, squid, jellyfish, coral and shrimp.

A reaction where energy is absorbed is called an endothermic reaction. These reactions typically experience a decrease in temperature. Changing from a solid to a liquid, or melting, absorbs energy---this is endothermic. All endothermic reactions absorb energy. They don’t all absorb energy as heat. The decomposition of water by electrolysis is another example. That powered the hydrogen fuel cell car.

Other examples of endothermic reactions The most important endothermic reactions on Earth is photosynthesis. The reaction is: 6CO2 + 6H2O → C6H12O6 + 6O2 Photosynthesis does not absorb energy as heat but as sunlight to turn carbon dioxide and water into oxygen and glucose. Most oxygen comes from the ocean (phytoplankton) rather than from the forests like we all usually think. But do save a tree!

Life and industry depend on chemical reactions. EX) Respiration-Process of getting energy from glucose (Opposite of Photosynthesis) Photosynthesis 6CO2 + 6H2O + energy → C6H12O6 + 6O2 Respiration C6H12O6 + 6O2 → 6CO2 + 6H2O + energy Catalysts---enzymes---make this process go quickly and automatically EX) Running a Car-Combustion reaction

Other Chemical Reactions Digestion Photosynthesis (gives you oxygen) Cooking Soap Fruits & Veggies Ripening

Uses in technology and industry Catalytic converters on our cars take unwanted waste products out of the combustion of gasoline so it is not emitted into our air. Silicon is extracted from quarts and microchips for computer and cell phones A material called photoresist is exposed to ultraviolet light producing a chemical reaction that is used in printing our newspapers and magazines.

review Absorb energy Endothermic reactions always: How are respiration and photosynthesis the opposite from each other? The reactants of one process are the products of the other process. Respiration is exothermic; photosynthesis is endothermic. Go to page 229 and answer questions 5-14.