Physical vs. Chemical Change How are they different?

Physical Change A change that alters the appearance of a substance, but does not make a new substance. The size or shape might change, but the particles are still the same –Ex: phase changes, tearing paper, crushing a can

Chemical Changes A change in matter that produces a new substance with new properties Both the physical and chemical properties of the substance will be changed! –Ex: photosynthesis, burning, tarnishing, cooking

Chemical Reactions A process in which substances undergo chemical changes If a chemical reaction happens, a chemical change has occurred!

Two Types of Chemical Reactions Exothermic Reaction: heat energy Exits –It feels warm –Temperature increases Endothermic Reaction: heat energy Enters –It feels cold –Temperature decreases

Law of Conservation of Matter Atoms can rearrange during a chemical reaction, but the amount that you start with is the amount that you end with. Nothing is CREATED nor DESTROYED!

Law of Conservation of Matter Regardless of how substances are changed, the amount of atoms remains the same Nothing is CREATED nor DESTROYED!

Chemical Equations A short, easy way to describe a chemical reaction, using symbols instead of words. To satisfy the Law of Conservation of Matter each side of a chemical equation must be balanced.

Parts of Chemical Equations Reactants: materials at the beginning of a reaction (LEFT) Products: the new materials at the end of an equation (RIGHT) Arrow: means “yields” or “produces” Plus sign: separates more than one reactant or product

Finding Balanced Equations Make a chart under the equation that lists the different element types Count the number of atoms of each element on the reactant side and the product side Any numbers that are not identical on both sides show that the equation is not balanced! Circle the equations below that ARE balanced:

Finding Balanced Equations H 2 + Cl 2  HCl H 2 + Cl 2  2HCl CH 4 + O 2  CO 2 + H 2 O CH 4 + 2O 2  CO 2 + 2H 2 O

Correcting Unbalanced Equations Copy the equation down correctly. Count the number of atoms on each side of the equation. (CHART to keep track!) Check metals first, non-metals second, Oxygen and Hydrogen last. NEVER change, remove, or add subscripts. Add or change coefficients. ALWAYS put coefficients in front of the formula. Never write them in the middle of a formula.

Practice Balancing __ Na + __ Cl 2 → __ NaCl __ H 2 + __ O 2 → __ H 2 O __ Li + __ O 2 → __ Li 2 O __ AlCl 3 → __ Al + __ Cl 2