CHEMICAL REACTIONS & EQUATIONS CHEMISTRY NOTES CHEMICAL REACTIONS & EQUATIONS

Signs Of Chemical Reaction 1. CHANGE IN TEMPERATURE A. Exothermic Reaction: releases energy in the form of heat. You can feel it getting “hotter”

Signs Of Chemical Reaction 1. CHANGE IN TEMPERATURE B. Endothermic Reaction_: absorbs heat energy from the reactants. It feels “cooler” than it did at the beginning

Signs Of Chemical Reaction 2. COLOR CHANGE - After mixing 2 things together, you see a color change (could also be physical)

Signs of a Chemical Reaction 3. GAS PRODUCTION: bubbles are seen forming or being released from the reaction (could also be physical if boiling)

Signs Of Chemical Reaction 4. SOLID PRODUCTION- a new, solid substance forms. If a solid is formed in a solution, the solid is called a Precipitate

Signs Of Chemical Reaction 5. CHANGE IN PROPERTIES- A chemical reaction has occurred if the REACTANTS of the reaction are DIFFERENT from the PRODUCTS of the reaction. (Can’t get it back to what it was before the reaction.)

Signs of a Chemical Reaction 6. LIGHT PRODUCTION- (Bioluminescent)

RULES OF CHEMICAL RXNS Starting chemicals, elements or substances are called REACTANTS, because they are going to react to form something new.

Rules Of Chemical Rxns Ending chemicals, elements or substances are called PRODUCTS, because they were produced in the reaction.

RULES OF CHEMICAL RXNS All the ATOMS found at the start of a reaction must be present at the end of a reaction. This is the Law of Conservation of Matter (Mass) All matter (measured as mass) in the reactants must be present (equal) in the products.

Factors that affect Reaction Rate 1. TEMPERATURE- Hotter-More energy, particles move faster and collide more often, reaction occurs faster (Colder- reaction occurs more slowly)

Factors that affect Reaction Rate 2. CONCENTRATION- More particles, more opportunity for particles to collide

Factors that affect Reaction Rate 3. PRESSURE – Increased pressure tends to make the molecules collide more often

Factors that affect Reaction Rate 4. SURFACE AREA- A finely divided powder reacts more quickly than the same material in a great big lump.

Factors that affect Reaction Rate 5. STIRRING AND SHAKING – allows the particles to collide more often

Factors that affect Reaction Rate 6. CATALYST- A Catalyst is a substance that alters the rate of the chemical reaction without being used up or permanently changed chemically (ENZYMES) It provides an alternative route (mechanism) that lowers the Activation Energy needed to undergo a successful collision.

Factors that affect Reaction Rate 7. PHYSICAL STATE – If particles are in the same phase, then it is easier for the particles to mix and react. Different states, then only the particles at the surface react.

CHEMICAL BONDS A chemical bond occurs between _______________. Bonds only involve _________________________

CHEMICAL BONDS Electrons can be transferred between atoms Called an _________ Bond Example:

CHEMICAL BONDS Electrons can be shared between atoms Called a __________ Bond Example:

CHEMICAL FORMULAS A shorter, easier way of showing chemical reactions using symbols instead of words ________________ – shows the ratio of elements in a compound

CHEMICAL FORMULAS Subscript numbers behind a symbol tell how many atoms of that element there are in the substance.

CHEMICAL FORMULAS Example: Hydrogen Peroxide’s name means 1 Hydrogen for every 1 Oxygen. The formula is H2O2

CHEMICAL FORMULAS What does “Carbon Dioxide” mean? What is its formula?

CHEMICAL FORMULAS What are other examples of formulas you can think of?

BALANCING EQUATIONS 1. Write the reaction in words. 2. Write the chemical equation.

BALANCING EQUATIONS 3. Count all of the atoms for each element on each side of the equation.

BALANCING EQUATIONS 4. Choose ___________ to place in front of each molecule to make each side of the equation balance.

Classifying Chemical Reactions Synthesis Decomposition Single Replacement Double Replacement

Synthesis Reaction Two or more elements combine to form a more complex compound A + B  AB Hand + kerchief  handkerchief Example: C + Cl2  CCl4

Decomposition Reaction Breaks down compounds into simpler substances AB  A + B Schoolbook  school + book Example: Al2O3  Al + O2

Replacement Reaction A reaction in which one element replaces another in a compound, or two elements in different compounds trade places AB + C  AC + B (Single) AB + CD  AC + BD (Double)