Chapter 1 Section 1: Matter & its changes Why are elements sometimes called the building blocks of matter?  All matter (anything that has mass and takes up space) is composed of one element or a combination of two or more elements

What is a compound?  A pure substance made of two or more elements that are combined chemically Ex. Sodium Chloride (table salt)

What is a Mixture?  Two or more substances (elements, compounds, or both) that are in the same place but not chemically combined  Solution: well-mixed mixture –i.e. Salt water

What is the difference between a physical and a chemical change?  A change in matter that produces one or more new substances is a chemical change, or chemical reaction  Physical change examples: braiding your hair, squashing a marshmallow  Chemical change examples: burning of gasoline, burning a marshmallow

How can you tell when a chemical reaction occurs?  Chemical changes occur when bonds break and new bonds form  Chemical reactions involve two main kinds of changes that you can observe-formation of new substances and changes in energy

What are some changes in properties that indicate a chemical change?  Precipitate – a solid that forms from a solution during a chemical reaction  Color change may indicate a chemical reaction  Gas production – bubbles

What are atoms and molecules?  An atom consists of a nucleus surrounded by one or more electrons  The smallest particle of an element  A molecule is the combination of 2 or more atoms  Ex. H 2 O

What is a chemical bond?  A chemical bond is the force of that holds atoms together  Some bonds are strong while others are weak  Reactions occur when bonds are formed or broken Covalent bond

Section 2: Describing chemical reactions What information does a chemical equation contain?  Chemical equations use chemical formulas and other symbols instead of words to summarize a reaction  Reactants – substances you have at the beginning  Products – new substances produced when the reaction is complete

What does the principle of conservation of mass state?  That in a chemical reaction, the total mass of the reactants must equal the total mass of the products  Matter is neither created nor destroyed

What does open or closed system mean?  Open system – matter can enter from or escape to the surroundings  Closed system – matter is not allowed to enter or leave

What must a balanced chemical equation show?  The same number of each type of atom on both sides of the equation  Represents the conservation of mass  Coefficients – a number placed in front of a chemical formula in an equation that tells you how many atoms or molecules of a reactant or product take place in the reaction

How do you balance chemical equations?  Count the # of atoms of each element in the reactants & products  ID element that is not equal on both sides  Add coefficient to the front of the formula that will make the # = on both sides for that element

Sample Problems Sample Problem: Zn + HBr  H 2 + ZnBr 2 Multiply HBr x 2 to correct (balance) Zn + 2HBr  H 2 + ZnBr 2 ReactantsProducts 1 Zn 1 H 2 H 1 Br 2 Br ReactantsProducts 1 Zn 2 H 2 Br

Try these!!  Na + Cl 2  NaCl  Ca + Cl 2  CaCl 2  H 2 O  H 2 + O 2  N 2 + H 2  NH 3  Al 2 O 3  Al + O 2  P 4 + O 2  P 4 O 6  Fe + H 2 O  Fe 3 O 4 + H

What are the three categories of chemical reactions?  Synthesis  Decomposition  Replacement

What is a synthesis reaction?  When two or more substances combine to make a more complex substance –A + B  AB –2H 2 + O 2  2H 2 O  Example: hydrogen and oxygen to make water

What is a Decomposition reaction?  Breaking down compounds into simpler products –AB  A + B –2H 2 O 2  2H 2 O + O 2  Example: Hydrogen peroxide decomposes into water and oxygen gas

What is a replacement reaction?  When one element replaces another in a compound, or when two elements in different compounds trade places  Example: copper metal obtained by heating copper oxide with carbon  Single (one element replaces another) –AB + C  AC + B –Zn + 2HCl  ZnCl 2 + H 2 or double (elements appear to trade places with another compound) –AB + CD  AC + BD –NaCl + AgF  NaF +AgCl

Section 3: Controlling Chemical Reactions How do you categorize changes in energy?  Endothermic – A reaction in which energy is absorbed –Examples: baking soda and vinegar gets cooler when combined  Exothermic – A reaction that releases energy in the form of heat –Examples: burning of airplane fuel

How is activation energy related to chemical reactions?  The minimum amount of energy needed to start a chemical reaction  All chemical reactions need a certain amount of activation energy to get started

What factors affect the rate of a chemical reaction?  Surface area – the greater the surface area that faster the reaction (ex. Chewing)  Temperature – raising the temperature causes particles to move faster and therefore have more energy; they also come into contact more often; lowering temperature slows things down  Concentration – amount of substance in a given volume; increased concentration-increased reaction  Catalysts – increases the rate of a reaction by decreasing the energy needed to start –Enzymes: biological catalysts  Inhibitors – material used to decrease the rate of reaction (ex. preservatives in food)