Chem +: Chapter 8: Chemical Reactions and Chapter 9: Stoichiometry

Reactants

Substances used or consumed

Products

Substances made

Balancing equations

Add coefficients, but don’t change the chemical formula. The coefficients can represent particles, moles, or liters if the substance is a gas.

Strategy for balancing combustion equations

Start by balancing carbon and finish with oxygen.

Writing equations

Use the correct formulas, use the appropriate symbols, and balance the equation using coefficients.

(s)

Symbol for a solid in an equation

(l)

Symbol for a liquid in an equation

(g)

Symbol for a gas in an equation

(aq)

Symbol for an aqueous solution, or something dissolved in water, in an equation.

→

Yield arrow, means forms or produces

↑

Forms a gaseous product

↓

Solid/precipitate forms

Δ

Heat applied

Diatomic Elements

Elements whose natural state must consist of two of the elements bonded to each other. These include H₂, O₂, N₂, Cl₂, Br₂, I₂, F₂. (Remember Dr. BRINCLHOF)

Catalyst

Matter or energy that speed up a reaction without being consumed or produced. They are written above the yield arrow. Heat, light, and some substances such as water, manganese dioxide, platinum, and palladium are common examples.

Synthesis

Two or more substances react to form one product.

Decomposition

One reactant is broked down into two or more products. Heat or other energy is usually needed to initiate the reaction.

Single Replacement (SR)

An element replaces another element in a compound. (AB + C → A + BC). More reactive elements replace less reactive elements. If C is less reactive than A, no reaction occurs. If C and A are metals, the activity series must be used. If C and A are nonmetals, more electronegative elements are more reactive.

Double Replacement (DR)

Metals in two compounds switch places. Takes place in an aqueous solution. One of the products forms a precipitate, gas, or water. The compound will form a precipitate if one of the products is slightly soluble or insoluble (use solubility chart.) (AB + CD → AD + CB)

Combustion

Hydrocarbon reacts with oxygen gas, producing carbon dioxide gas and water gas. Exothermic (produces heat.) Requires activation energy.

Complete Ionic Equation

Shows all soluble substances (those in aqueous solutions) as ions.

Net Ionic Equation

Removes the substances repeated on both sides of the Complete Ionic Equation. Spectator ions are removed.

Mole Ratio

Comparison of the number of moles of any two substances in a reaction. Determines the amount of reactant needed or amount of product made by a reaction. They come from the coefficients from the balanced equations.

Basic stoichiometry steps

1. **START WITH A BALANCED EQUATION**
2. Start a molar conversion with the given value
3. Convert to moles
4. Use the mole ratio to convert the original substance to the substance you want to find.
5. Convert to the desired unit

Percent Yield

Comparison of experimental (lab) yield to the theoretical (stochioemtric prediction) yield

Limiting Reactant (LR)

Reactant that is completely consumed. Determines how much product is made.

Excess Reactant (ER)

Reactant that is not used up. Some will be left over.

Steps for determining the LR

1. Convert given A to given B, which is the amount you need to react.
2. Compare the B-value you calculated to the given B value


1. If the calculated B-value is greater than the given B value, then element B is the Limiting Reactant
2. If the calculated B-value is less than the given B value, then element A is the Limiting Reactant
3. You will then use the Limiting Reactant to solve the problem