Chemical Reactions

Unit Review Sheet

Facts and Definitions

Lesson 1: Atomic Theory and Chemical Formulas

• Atomic theory is a set of assumptions about the nature of atoms and elements. These assumptions include the following:
  • all matter is made of atoms,
  • atoms are divisible and are made up of subatomic particles that include a nucleus containing neutrons and proton and outer shells containing electrons,
  • all atoms of a given element are identical and weigh the same, and
  • compounds are formed by a combination of two or more different types of atom.
• A chemical reaction is a change of one substance into a new one that has a different arrangement of atoms.
• A closed system is a system that can exchange energy as heat, but not matter, with its surroundings.
• Conservation of mass is a principle that the total mass of an isolated or closed system remains constant, in spite of any physical or chemical changes that may take place.

Lesson 2: Chemistry and Patterns

• A chemical reaction changes the make-up of a substance by redistributing atoms or groups of atoms to make one or more new products.
• A reactant is a substance that reacts with another in a chemical reaction.
• A product is something that is made or created by a chemical reaction.
• A substance's physical properties are those that can be observed and measured without changing the chemical makeup of the substance (examples include texture, color, boiling point, and density).
• A physical change is a change to a substance's physical property that does not change its chemical composition; these changes do not produce a new substance (examples include crushing, freezing, and condensation).
• A substance's chemical properties are those that can be observed only during a chemical reaction (examples include flammability and ability to react with certain chemicals).

Lesson 3: Understanding Reactions

• The law of conservation of matter states that during a chemical reaction, the total number of atoms remains the same, so the total mass also remains constant, in spite of any physical or chemical changes that may take place.

Lesson 4: Combustion and Extinguishers

• Combustion is a chemical process in which a substance reacts vigorously with oxygen to produce heat and light, seen as a flame.
• An absorbent substance is capable of soaking up liquid.
• Capillary action is a phenomenon in which a liquid's surface rises, falls, or becomes distorted in shape when in contact with a solid.
• Oxidation is a chemical reaction in which oxygen is added to an element or compound.
• An endothermic reaction absorbs heat from its surroundings.
• An exothermic reaction gives off heat to its surroundings.

Lesson 5: Acids and Bases

• An acid is a compound that releases hydrogen ions (H+) to form a solution with a pH of less than 7.
• A base is a compound that releases hydroxide (OH-) ions to form a solution with a pH greater than 7.
• An ion is an atom or group of atoms that has acquired an electric charge by losing or gaining one or more electrons.
• A neutral compound is neither an acid not a base. It has a pH of 7.
• pH is a measure of whether a substance is acidic (an acid), alkaline or basic (a base), or neutral (neither acid nor base).

Lesson 6: Physical and Chemical Properties, Part I

• A physical change is one that alters the physical properties of a substance, such as state or size, but does not change its identity.
• A chemical change is a chemical reaction in which a substance loses its characteristics and becomes one or more new substances.
• A catalyst is a compound that helps to speed up a chemical reaction, but doesn't get consumed during the process.
• Specific heat is the amount of heat needed to raise the temperature of one gram of a substance by one degree Celsius.
• Chemical reactivity is a process that changes the molecular composition of a substance by redistributing atoms or groups of atoms without altering the structure of the nuclei of the atoms.

Lesson 7: Physical and Chemical Properties, Part II

• Decomposition is the process of breaking something down into smaller or simpler parts.
• Electrical conductivity is the ability of an object or substance to transmit electricity.
• Electrolyis is the conduction of electricity through something melted or dissolved in order to prompt decomposition of the melted or dissolved chemical into individual components.
• Magnetism is the phenomenon of physical attraction for iron, inherent in magnets or induced by a moving electric charge or current.
• Solubility is the extent to which one substance is able to dissolve in another.
• A solute is a substance dissolved in another substance; a solvent is a substance able to dissolve other substances; and a solution is a substance consisting of two or more substances mixed together and evenly dispersed.

Lesson 8: Periodic Characteristics

• Acids release hydrogen ions to form a solution with a pH of less than 7; acids react with a base to form a salt.
• Bases (or alkali) are water-soluble chemicals that react with acids to form salts; they have a pH above 7.
• A salt is a crystalline compound formed from the neutralization of an acid by a base. A salt contains a metal or an element in a group acting like a metal.
• Neutralization is to reduce a substance so that it is neither an acid nor alkaline (base).
• Precipitates are solids that separate out from a solution as a result of a chemical reaction.

Lesson 9: Scientific Argumentation

• A claim is a testable statement made regarding a particular idea. (Example: The amount of carbon dioxide in soda determines whether it is flat or fizzy. More carbon dioxide in the soda means more fizz.) The claim can be shown to be true or false.
• Evidence is data collected through experimentation; it is factual information without any value judgment regarding what it means.
• Justification is the acceptance or rejection of the initial claim supported by the evidence collected.

Lesson 10: Synthetic or Natural?

• A natural substance is one that is present in or produced by nature.
• A synthetic substance is one that is made artificially by chemical synthesis, often to resemble a natural product.
• A value judgment is an opinion formed after consideration of information or evidence.
• Toxicity is the degree to which something is poisonous.
• An antipyretic is a substance that reduces fever.
• An anti-inflammatory is a substance that reduces swelling.
• A phytochemical is a naturally occurring plant substance shown by research to protect against disease.
• ADR stands for an adverse drug reaction, and is also known as a side effect.
• An analgesic is a substance that reduces pain without causing a person to become unconscious.

Final Project: Chemistry in Action

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