Do Now: (this problem is in your packet)

Ribose is an important sugar found in DNA and RNA. Ribose has a gram molecular mass of 150 g/mol and an empirical formula of CH2O. What is the molecular formula for ribose?

Chemical Equations

What are they?

Def: represents, with symbols and formulas, the reactants and products of a chemical reaction

• Details the ratios of the substances that react.

• Equation must contain the correct formulas of reactants and products

Law of Conservation of Mass

• matter cannot be created or destroyed• same # of atoms of each element must

be written as products and reactants• coefficients are written to equalize the

number of atoms of each element (coefficients – numbers placed before chemical formulas)

Balancing chemical equations

1. Identify the names of reactants and products.Ex) Sodium metal reacts with chlorine gas to form sodium

chloride

Sodium + Chlorine sodium chloride 2. Substitute the correct symbols and formulas

 Na (s) + Cl2 (g) NaCl (s)

Keep it going!

3. Balance the number of atoms of each element by changing coefficients only!•subscripts MAY NOT be changed for a chemical, this will change the identity of the substance

___Na (s) + ___Cl2 (g) ___ NaCl (s)4. count the number of atoms of each element to be sure the equation is balanced.

Helpful Hints

• When polyatomic ions appear the same on both sides of the equation, count them as only one item

When water is formed or decomposed from hydrogen and a hydroxide ion, write the water in as HOH

ExampleAluminum + hydrogen nitrate Aluminum nitrate + hydrogen

Example

Na + H2O H2 + NaOH

Example

MgCl2 + Na2CO3 MgCO3 + NaCl

Types of Chemical Reactions1.  Synthesis Rxns (combination) – two or

more substances combine to form a single new substance

General formula: A + B → AB

Synthesis Reaction ExamplesMg(s) + O2(g) MgO(s)

Na(s) + S(l)

CaO(s) + H2O(l)

SO3(g) + H2O(l)

2. DecompositionDef: a single compound is broken down into

two or more products

General formula: AB → A + B

Decomposition Reaction Examples

[electrolysis] electricity

H2O (l) H2(g) + O2(g) electricity

NaCl (l)

Decomposition Reaction Examples

Decomposition of carbonates Heat, D

CaCO3(g) CaO(s) + CO2(g)

heat

Sodium carbonate

Decomposition Reaction Examples

Decomposition of metal hydroxidesheat

Mg(OH)2(s) MgO(s) + H2O(l)

heat

Ba(OH)2

Decompostion of metal chlorates

heat

NaClO3(s) NaCl(s) + O2(g)

heat

KClO3

3. Single Replacement RXNSDef: one element replaces a second element in

a compound

• metals replace metals

• nonmetals replace nonmetals

General Formula: A + BC → AC + B

How does it work?

• check Table J – Activity series• more active metals replace less active metals • (elements can only replace other elements

that are lower on Table J)• more active nonmetals replace less active

nonmetals

Metals replacing less active metals

Mg(s) + Zn(NO3)2(aq) Mg(NO3)2(aq) + Zn(s)

Zn(s) + AgNO3(aq)

Zn(s) + CaSO4

Replacement of halogens

Cl2(g) + KI(s) I2(s) + NaF

Replacement of H in water by a metal

K(s) + H2O

Replacement of hydrogen in an acid by a metal

Zn(s) + HCl(aq)

4. Double replacement reactions Def: involves the exchange of positive ions

between two reacting aqueous compounds

General Formula: AB + CD → AD + CBproducts typically include:• a precipitate (nearly insoluble compound)• an insoluble gas (bubbles out of solution)• a molecular compound (usually water)

ExamplesPb(NO3)2(aq) + KI(aq) PbI(s) +

2KNO3(aq) FeS(s) + HCl NaCl + AgNO3 HNO3 + KOH

Predict the products andBalance this puppy!

Ba(OH)2 + H3PO4 →

5. Combustion RxnsDef: an element or a compound reacts with

oxygen producing heat and light

hydrocarbons burn completely to form water and carbon dioxide

ExamplesC2H6(g) + O2(g)

C8H18 + O2

Mass Relationships in Chemical Reactions

• Stoichiometry is the term used to describe the mass relationships in chemical reactions.

The coefficients in a balanced chemical equation represent the mole to mole ratio of the reactants and products

• the relative amount of reactant needed or product formed in a chemical reaction can be determined by stoichiometry (the equation acts like a recipe for the reaction that takes place)

N2 + H2 → NH3

After balancing the equation, how many moles of H2 are consumed in the reaction? ____

How many moles of NH3 are produced? _____

Therefore, there is a ______ : _______ ratio of H2 to NH3.

Calculating the # of moles consumed or produced according to a chem equation:

1. Balance the equation.2. Write the given quantity from the question

above that substance in the equation. Place an X above the substance that you are trying to find.

3. Establish a ratio of the given quantity to the balanced coefficient for each substance in question.

4. Cross multiply to solve for X.

N2 + H2 → NH3

If 2 moles of N2 react completely:a. How many moles of hydrogen must react?

b. How many moles of ammonia will be produced?

C2H6 + O2 CO2 + H2O

a. How many moles of CO2 are produced when 1 mole of ethane (C2H6) is consumed?

b. How many moles of O2 are consumed when 5

moles of water are produced?

The following balanced equation shows the complete combustion of octane. Gasoline is a complex mixture of many chemicals. For the purpose of this calculation, we will assume that gasoline is comprised entirely of a compound called octane.

2 C8H18 + 25 O2 → 16CO2 + 18H2O

2 C8H18 + 25 O2 → 16CO2 + 18H2O

• How many moles of octane (C8H18) are there in 10.0 gallons (26,714g)?

2 C8H18 + 25 O2 → 16CO2 + 18H2O

• Use the balanced equation to determine how many moles of CO2 are produced when all of the octane in the previous question is completely consumed?

When 2.0 mol of octane are burned 10943 kj of heat are

produced. How many grams of water at 100 degrees Celsius can

be boiled?