L6 Chemical Reactions

Synthesis Reactions (Combination Reactions)

Reactions where two or more reactants combine to form one product, following the general format $A + B \rightarrow AB$.

Decomposition Reactions

A reaction where one reactant decomposes to become two or more products, following the general format $AB \rightarrow A + B$.

Single Displacement Reactions (Single Replacement Reactions)

A reaction where an uncombined element displaces or takes the place of an element within a compound; characterized by an element and a compound as reactants and a different element and compound as products.

Double Displacement Reactions (Double Replacement Reactions)

Reactions where the positive ions in two reacting compounds switch partners, following the general format $AB + CD \rightarrow AD + CB$.

Combustion Reactions

A reaction commonly called burning in which $O_2$ reacts with a hydrocarbon compound (fuel), and the products are $CO_2$ and $H_2O$.

Acid-Base Reactions (Neutralization Reactions)

A specific type of double displacement reaction where an acid (hydrogen ion $H^+$ in front) and a base (hydroxide ion $-OH$ in back) react to form a salt and water ($H_2O$).

"San Diego San Diego, CA"

A mnemonic to help remember the six types of chemical reactions.

Hydrocarbon

A compound (referred to as fuel) that reacts with oxygen in a combustion reaction to produce carbon dioxide and water.

Exothermic

A term describing reactions that produce energy, such as combustion reactions.

Synthesis General Format

$$A + B \rightarrow AB$$

Decomposition General Format

$$AB \rightarrow A + B$$

Single Displacement General Format (Positive Charge)

$A + BX \rightarrow AX + B$; used if the element takes on a positive charge in compounds.

Single Displacement General Format (Negative Charge)

$A + YB \rightarrow YA + B$; used if the element takes on a negative charge in compounds.

Double Displacement General Format

$$AB + CD \rightarrow AD + CB$$

Combustion General Format

$C_xH_y + O_2 \rightarrow CO_2 + H_2O$ (Fuel + $O_2 \rightarrow CO_2 + H_2O$)

Acid-Base General Format

$$H-X + Y-OH \rightarrow YX \text{ (a salt)} + H_2O \text{ (water)}$$

Physical changes

Changes that do not alter the chemical composition of a substance, such as boiling water.

Chemical changes

Changes that do alter the chemical composition of a substance, such as forming water from hydrogen and oxygen.

Chemical reaction

The formation of new substances, also known as the products, from a set of reactants.

Precipitate

A solid that forms during a chemical reaction.

Exothermic

A condition where heat is produced during a reaction.

Endothermic

A condition where heat is absorbed during a reaction.

Chemical equation

A short-hand method used to represent the reactants and products in a chemical reaction.

Reactants

The substances in a chemical reaction always located on the left side or before the arrow.

Products

The substances in a chemical reaction always located on the right side or after the arrow.

$$\rightarrow$$

A sign in a chemical equation that means "reacts to form" or "to produce".

$$(s)$$

A symbol used in a chemical equation to indicate that the chemical is in a solid phase.

$$(l)$$

A symbol used in a chemical equation to indicate that the chemical is in a liquid phase.

$$(g)$$

A symbol used in a chemical equation to indicate that the chemical is in a gas phase.

$$(aq)$$

A symbol used in a chemical equation to indicate that the chemical is aqueous or dissolved in water.

Coefficients

Numbers added in front of chemical formulas to ensure the same number of atoms are on each side of the equation.

Law of Conservation of Matter

The principle stating that matter cannot be created or destroyed, which requires chemical equations to be balanced so that the number of each type of atom is the same on both the reactant and product sides.

Reactants

The substances written to the left of the arrow in a chemical equation.

Products

The substances written to the right side of the arrow in a chemical equation.

Coefficients

The numbers placed in front of the chemicals (reactants and products) in an equation to balance the number of atoms on each side.

Balanced Equation

A chemical equation, such as $C + O_2 \rightarrow CO_2$, where there is one carbon and two oxygens on each side, regardless of what they are bonded to.

Trial-and-error method

A technique used to balance simple chemical reactions by adjusting coefficients until the number of atoms of each element is equal on both sides of the equation.

Multiplication method

A more structured method for balancing complex chemical equations that involves listing atoms under the reaction arrow and using multiplication to find the correct coefficients.

Dihydrogen monoxide

The product formed from the reaction between hydrogen gas and oxygen gas, represented by the chemical formula $H_2O$.

Single displacement reaction

A type of reaction specifically mentioned in the practice examples involving the reaction between sodium metal and hydrogen chloride.

Potassium chlorate ($KClO_3$)

A compound used in the text's detailed balancing example that decomposes into potassium chloride ($KCl$) and oxygen ($O_2$).

Phosphorus pentoxide ($P_4O_{10}$)

The product formed in the example reaction $4P + 5O_2 \rightarrow P_4O_{10}$ used to illustrate the trial-and-error balancing method.

Endothermic Reaction

A reaction where heat is absorbed and used as a reactant.

Exothermic Reaction

A reaction where heat is released and produced as a product.

Heat of Reaction (Enthalpy Change)

The measure of the amount of heat that flows during a chemical reaction, represented by the symbol $\Delta H$.

$$\Delta H$$

The symbol representing the heat of reaction or enthalpy change.

Positive $\Delta H$

Indicates the reaction is endothermic and heat is absorbed (e.g., $\Delta H = +180.5\,kJ$).

Negative $\Delta H$

Indicates the reaction is exothermic and heat is released (e.g., $\Delta H = -393\,kJ$).

Heat as a Reactant

The representation within an equation for an endothermic reaction, such as $\text{heat (kJ)} + AB \rightarrow A + B$.

Heat as a Product

The representation within an equation for an exothermic reaction, such as $A + B \rightarrow AB + \text{heat (kJ)}$.

$$N_2 + O_2 + 180.5\,kJ \rightarrow 2NO$$

An example of an endothermic reaction where the heat term is shown within the equation as a reactant.

$$C + O_2 \rightarrow CO_2 + 393\,kJ$$

An example of an exothermic reaction where the heat term is shown within the equation as a product.

Chemical kinetics

The study of the rates of chemical reactions, ranging from almost instantaneous explosions to unnoticeably slow corrosion.

Reaction rate

The speed at which a reaction can take place, characterized by the rate at which the concentrations of reactants and products change.

Temperature (factor)

A factor where an increase causes molecules to move faster, leading to more collisions between reactant particles and speeding up the reaction.

Concentrations of Reactants

A factor where the reaction occurs faster when there are more reactants because more collisions between reactant particles will occur.

Activation energy

The energy needed to break apart bonds of the reacting molecules.

Catalysts

An additional ingredient or energy addition that gives the reaction an alternate method of occurring with lower activation energy, causing products to form faster.