Chemical Reactions Chapter 2 Sections 1-4 Pages 26-51

Chemical Reactions A chemical change This is an example of a Chemical Reaction. A chemical reaction is The chemical and physical properties of the new substances differ from those of the original substances. More examples: Baking bread (yeast), baking muffins (baking soda), leaves changing color, metal rusting, burning wood..

Signs of a Chemical Reaction Gas formation Forming a precipitate (a solid substance that forms in a solution) …

A change in Properties The sure sign for a chemical reaction is the formation of a ____ _________.

Bonds…Chemical Bonds… A chemical bond is a force that holds two atoms together in a molecule. For a chemical reaction to take place, the

Breaking and Making Bonds The chemical bonds in the starting substances _______, and then ____ bonds form to make new substances.

New Bonds, New Substances New properties form as a result of a new substance. Don’t forget that the new properties are ____ _______ from the original.

Chemical Formulas A chemical formula is a shorthand way to use chemical symbols and numbers to represent a substance. It shows how many atoms of each kind are present in a molecule. A subscript is If there is no subscript then only one atom of that element is present.

Formulas for Covalent Compounds Usually composed of two ________ Use _______, to represent a number. Prefixes tell you how many atoms of each element are in a formula. mono- 1, di- 2, tri- 3, tetra- 4, penta- 5, etc.

Formulas for Ionic Compounds Usually a _____ and a _________. Charge must be ______ or ___. The formula must have subscripts that cause the charges of the ions to ______ _____.

Chemical Equations A chemical equation uses chemical symbols and formulas as a shortcut to describe a chemical reaction. Reactants: Products: The arrow represents the equal sign.

Importance of Accuracy The correct symbols or formula is important There are examples of similar symbols and formulas that are very different: – CO₂ – CO – Co

Law of Conservation of Mass Equations must be balanced! ________ in the 1700s found that the total mass of the reactants are always the same total mass of the products. The law states that This law means that a chemical equation must show the same numbers and kinds of atoms on both sides of the arrow.

How to Balance an Equation 1.Count 2. Multiply 3. Make sure 4. Then

Balancing Equations Animation flash- animation.com/chemistry_interactive/basic_c hemical_reaction_balance_learning.htm flash- animation.com/chemistry_interactive/basic_c hemical_reaction_balance_learning.htm

Balancing Equations ndex.html ndex.html ml ml See extra power point on balancing equations on web site.

Types of Chemical Reactions Synthesis Reaction: a reaction in “two coming together to dance” Decomposition Reaction: a reaction in (opposite of synthesis) “the two ending the dance and separate”

Types of Chemical Reactions Single Displacement Reaction: a reaction in (Usually the more reactive element does the replacing) “one person cutting in on a couple dancing, leaving one person alone” Double Displacement Reaction: a reaction in “trade partners”

Exothermic & Endothermic Reactions Exothermic reactions give off energy. Energy is ________. Energy is a ________. 2Na + Cl₂ →2NaCl + energy Endothermic reactions ______ __ energy. Energy is required. Energy is written as a _______. Example is photosynthesis 6CO₂ + 6H₂O + energy → C₆H₁₂O₆ + 6O₂ Carbon Dioxide, water and sunlight → glucose and Oxygen

The Law of Conservation of Energy Energy is Energy can be _______.

Rates of Reactions A reaction can only take place if the Must be energy to break the bonds. The is called the rate of reaction.

Activation Energy Activation energy is F E L Looking at energy diagrams- you can tell if it energy is given off if the reactants have a higher energy than the products (page 45)

Factors that Increase the Rates of Reaction T (particles increase movement) H (because there are more reactants colliding) S (exposes more particles of the reactants to the other reactants) C can speed up reaction without itself changing (example enzymes in body or catalytic converter in car)

Factor that Decreases Rates of Reaction ________ slow down or stops a chemical reactions. Food preservatives Antibiotics