Chemical reactions: Section 4.1 answers to vocabulary
Chemical reaction • Occurs when two or more substances combine to form new substances. • Examples: • Space shuttle • Air bags • Baking soda and vingar • Mentos and diet coke
When a chemical reaction occurs, a new substance forms and evidence of the reaction may include one or more of the following: • A color change • The formation of an odour • The formation of a solid or gas • The release or absorption of heat
Reactants • The materials at the start of a reaction • The substance that reacts with another substance to create something new. • Examples: • Burning wood: the log and oxygen • Rocket science: Alka seltzer and vinegar
Products • The new materials produced by a reaction. • Examples: • Burning wood: carbon dioxide, water, energy released • Rocket science: • NaC2H3O2(aq) + H2O(l) + CO2(g)
Chemical word equation • The reactants always appear on the left of the arrow • The products are always on the right of the arrow • The arrow indicates the direction in which the reaction is most likely to occur. • Example: • Log + oxygen carbon dioxide + water + energy released • Alka seltzer + vinegar NaC2H3O2(aq) + H2O(l) + CO2(g)
Exothermic reaction • A chemical reaction that RELEASES (or give off) heat energy • Examples: • Fire • When your body is metabolizing food • Combustion reactions (considered the first chemical reaction used by humans.) • Fireworks • Combustion engines
Endothermic reactions • A chemical reaction in which heat energy is ABSORBED. • Examples: • Chemical cold packs – energy is absorbed from the liquid in the bag, and the pack becomes very cold. • Baking soda and vinegar - temp decreases.
Combustion • A chemical reaction that occurs when oxygen reacts with a substance to form a new substance and gives off energy. • Therefore, always exothermic (give off energy!) • Examples: • Burning wood: Log + oxygencarbon dioxide + water + energy released • Internal combustion engine: a fuel, such as gasoline, fills a chamber mixed with air (oxygen) and then is ignited by a spark plug, causing a small explosion (heat released) which generates work.
Corrosion • The slow chemical change that occurs when oxygen in the air reacts with a metal. • Examples: • Rust: Iron + oxygen Iron oxide • Tarnished silver
Cellular respiration • A chemical reaction that takes place in the cells of your body. • Example: • In your cells • Food + Oxygen carbon dioxide + water + energy