Chemical Reactions and Equations

Vocabulary flashcards on core concepts of chemical reactions, types of changes, characteristics, balancing equations, and chemical notation conventions based on lecture notes.

Change

A transformation in the physical or chemical properties of a substance.

Physical Change

A change in which the identity of the substance remains the same, and only its physical properties (such as shape, size, and state) are altered, such as the melting of ice or boiling of water.

Chemical Change

A change that leads to the formation of a new substance with different properties, such as the rusting of iron or burning of paper.

Burning of a Candle

A process involving both physical and chemical changes; the melting of solid wax to liquid wax is a reversible physical change, while the burning of wax into carbon dioxide and water vapour is an irreversible chemical change.

Chemical Reaction

A process in which substances undergo a transformation, resulting in the formation of new substances with different chemical properties.

Chemical Equation

A representation of a chemical reaction using symbols and chemical formulae to show the reactants and products involved.

Characteristics of Chemical Reactions

Observable evidence that a chemical reaction has occurred, which includes change in color, change in temperature, change in state, evolution of gas, and formation of a precipitate.

Precipitate

An insoluble solid that settles down after the completion of a chemical reaction.

Exothermic Reaction

A chemical reaction that releases heat energy.

Endothermic Reaction

A chemical reaction in which heat energy is absorbed.

Catalyst

A substance that speeds up a chemical reaction, or lowers the temperature or pressure needed to start one, without itself being consumed during the reaction.

Word Reaction

A chemical reaction written out in word form, expressed as $\text{Reactants} = \text{Products}$ (e.g., $\text{Magnesium} + \text{Oxygen} \rightarrow \text{Magnesium oxide}$).

Skeletal Chemical Equation

An unbalanced chemical equation in which the number of atoms of each element on the reactant side is not equal to the number of atoms on the product side (e.g., $\text{Mg} + \text{O}_2 \rightarrow \text{MgO}$).

Law of Conservation of Mass

A fundamental law stating that in simple chemical reactions, mass is neither created nor destroyed, requiring the mass of reactants to equal the mass of products and the number of atoms of each element to remain equal on both sides of the equation.

Subscript Rule in Balancing

The requirement that the subscript of a chemical symbol or formula must not be changed in order to make the number of atoms equal on both sides of a chemical equation.

Initial Balancing Priority

The method of beginning the balancing process with the compound that contains the maximum number of atoms, and balancing the element with the maximum number of atoms within that compound first.

Upward Arrow ($\uparrow$)

A notation used in a chemical equation to indicate that a gas is evolved during the reaction.

Downward Arrow ($\downarrow$)

A notation used in a chemical equation to indicate that a precipitate is formed during the reaction.

Reaction Condition Notations

Information such as heat, pressure, or catalysts written above or below the reaction arrow to specify the exact conditions under which a chemical reaction occurs.