Chemical Reactions Chapter 2 Section 1

Review… Chemical Bond is a force that holds two atoms together CHEMICAL REACTION A process in which one or more substance change to make one or more new substances

Physical Background Physical Property: Characteristics of matter that can be seen through direct observations Density Melting point Boiling Point Physical Change: Change in which the identity of the substance does not change

Chemical Background Chemical Property: characteristics that can only be observed when one substance changes into a different substance –Iron to Rust Chemical Change: New Substance is formed

A Change of Properties The properties of these substances are very different from the starting substances In a chemical reaction –bonds are broken –atoms are rearranged –new bonds are formed

Signs of a Chemical Reaction Gas Formation Solid Formation –Percipitate Energy Change –Endothermic –Exothermic Color change

Chemical or Physical Glass Breaking Hammering wood together Burning Leaves Melting Ice Frying an egg Melting butter Bleaching your hair Fireworks Mixing salt with water

Math Practice 1.3(2)= 2.4(2+3a)= 3.1(3a+4b)= 4.2(2a+3b+5c)=

Chemical Formula A shorthand way to use chemical symbols and numbers to represent a substance Shows how many of each atom is present in a molecule –H2O–H2O

Chemical Formula Shows how many of each atom is present in a molecule –3H 2 O Subscript 2 – (applies to symbol before it) Coefficient 3 – (applies to entire molecule)

4 Mg: 4 Cr: 4 O:16 C: 30 H: 60 O:30 Mg:2 Cl:4 H:6 S:3 O:12 O:2 H:2 Cl:

Be Accurate Symbols can be mistaken!!

Use chemical symbols and formulas as a shortcut to describe a chemical reaction Reactants = starting material Products = substances formed from a reaction C + O 2  CO 2 reactants before arrow products after arrow Chemical Equations

Law of conservation of mass During a reaction, mass is neither created nor destroyed Equations must be balanced because atoms are neither created nor destroyed Mass of Reactants = Mass of Products

Chemical Equation Shows the reaction between reactants and products Reactants-starting material Products-what is formed C + O 2 CO 2 C=1C=1 O=2O=2

Balancing Chemical Equations

Example: Mg + O 2  MgO Then all you do is list the atoms that are involved on each side of the arrow Mg + O 2  MgO Mg O Mg O

[1] Just count up the atoms on each side Then start balancing: Mg + O 2  MgO Mg O [2] The numbers aren’t balanced so then add Coefficient to make up for any shortages And adjust totals Mg + O 2  MgO Mg O Mg O

Mg + O 2  MgO Mg O But the numbers still aren’t equal, so add another Coefficient 2 And adjust totals again NOW BOTH SIDES HAVE EQUAL NUMBERS OF ATOMS WE SAY THAT THE EQUATION IS BALANCED!! 2

Try to balance these equations using the same method: [1] Na + Cl 2  NaCl [2] CH 4 + O 2  CO 2 + H 2 O [4] Al + O 2  Al 2 O 3 [3] Li + HNO 3  LiNO 3 + H 2

[1] 2 Na + Cl 2  2 NaCl [2] CH O 2  CO H 2 O [4] 4 Al + 3 O 2  2 Al 2 O 3 [3] 2 Li + 2 HNO 3  2 LiNO 3 + H 2 Here are the answers: HOPE YOU’VE GOT THE IDEA… REMEMBER TO CHECK THAT YOU CAN DO ELECTROLYSIS EQUATIONS TOO