Unit 2: Chemical Formulas and Reactions Overview
(8.5D) Chemical Formulas
(8.5D) Students will recognize that chemical formulas are used to identify substances and determine the number of atoms of each element in chemical formulas containing subscripts.
- Chemical formula - a combination of element symbols and subscript numbers used to show the composition of a substance, either as a compound or in pure element form. Chemical formulas make it easier to describe substances by providing information about the number and kinds of atoms that create a molecule of that substance.
- Subscript - The small number following the symbol of an element that shows how many atoms of that element are in the molecule (no # means there is 1 atom)
- Coefficient - The number that comes before a chemical formula and shows how many molecules are involved in a reaction
- Molecule - Two or more atoms that are bonded together (can be 2 of the same element or 2 different elements)
- Element - A pure substance that cannot be broken down into other substances.
- Compound - A substance composed of two or more elements.
- Reactant - Substances that are present before a chemical reaction occurs.
- Product - Substances that are produced from a chemical reaction.
- Law of Conservation of Mass - Matter is neither created nor destroyed, only rearranged. The mass of all reactants must equal the mass of all products.
- Chemical Equation - Shows the formulas for the reactants and products in a chemical reaction
(8.5E) Chemical Reactions
8.5E Students will investigate how evidence of chemical reactions indicates that new substances with different properties are formed and how that relates to the law of conservation of mass
- Reactant - Substances that are present before a chemical reaction occurs.
- Product - Substances that are produced from a chemical reaction.
- Law of Conservation of Mass - Matter is neither created nor destroyed, only rearranged. The mass of all reactants must equal the mass of all products.
- Chemical Reaction - When atoms of at least two different substance rearrange to form new and different substance.
- Physical Change - A change in matter that only affects the appearance of the substance
- Chemical Change - A change in matter which results in a new and different substance being formed
- Chemical Reaction Evidence:
- Precipitate - Two liquids combine and form a solid. Example: Magnesium and Calcium in treated water combine, become solid, and clog sink drains.
- Odor Change - A smell is produced. Example: Smelling food cooking.
- Color Change - An unexpected color change occurs. Example: Iron rusting.
- Gas Formation - Bubbles or fizzing occur. Example: Alka Seltzer tablet in water.
- Energy release/absorption - Light or sound is produced. Example: Breaking a glow stick to produce a glow.
- Temperature change - Temperature unexpectedly increases or decreases. Example: Instant heat or cold packs.