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 CH 2 O. 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) + Cl 2 (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) + ___Cl 2 (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

Example Aluminum + hydrogen nitrate  Aluminum nitrate + hydrogen

Example Na + H 2 O  H 2 + NaOH

Example MgCl 2 +Na 2 CO 3  MgCO 3 + NaCl

Types of Chemical Reactions 1. Synthesis Rxns (combination) – two or more substances combine to form a single new substance General formula: A + B → AB

Synthesis Reaction Examples Mg(s) + O 2 (g)  MgO(s) Na(s) + S(l)  CaO(s) + H 2 O(l)  SO 3(g) + H 2 O (l) 

2. Decomposition Def: a single compound is broken down into two or more products General formula: AB → A + B

Decomposition Reaction Examples [electrolysis] electricity H 2 O (l)  H 2 (g) + O 2 (g) electricity NaCl (l) 

Decomposition Reaction Examples Decomposition of carbonates Heat,  CaCO 3 (g)  CaO(s) + CO 2 (g) heat Sodium carbonate 

Decomposition Reaction Examples Decomposition of metal hydroxides heat Mg(OH) 2 (s)  MgO(s) + H 2 O(l) heat Ba(OH) 2 

Decompostion of metal chlorates heat NaClO 3 (s)  NaCl(s) + O 2 (g) heat KClO3 

3. Single Replacement RXNS Def: 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(NO 3 ) 2 (aq)  Mg(NO 3 ) 2 (aq) + Zn(s) Zn(s) + AgNO 3 (aq)  Zn(s) + CaSO 4 

Replacement of halogens Cl 2 (g) + KI(s)  I 2 (s) + NaF 

Replacement of H in water by a metal K(s) + H 2 O  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 + CB products typically include: a precipitate (nearly insoluble compound) an insoluble gas (bubbles out of solution) a molecular compound (usually water)

Examples Pb(NO 3 ) 2 (aq) + KI(aq)  PbI(s) + 2KNO 3 (aq) FeS(s) + HCl  NaCl + AgNO 3  HNO 3 + KOH 

Predict the products and Balance this puppy! Ba(OH) 2 + H 3 PO 4 →

5. Combustion Rxns Def: an element or a compound reacts with oxygen producing heat and light hydrocarbons burn completely to form water and carbon dioxide

Examples C 2 H 6 (g) + O 2 (g)  C 8 H 18 + O 2 

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)

N 2 + H 2 → NH 3 After balancing the equation, how many moles of H 2 are consumed in the reaction? ____ How many moles of NH 3 are produced? _____ Therefore, there is a ______ : _______ ratio of H 2 to NH 3.

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.

N 2 + H 2 → NH 3 If 2 moles of N 2 react completely: a.How many moles of hydrogen must react? b. How many moles of ammonia will be produced?

C 2 H 6 + O 2  CO 2 + H 2 O a. How many moles of CO 2 are produced when 1 mole of ethane (C 2 H 6 ) is consumed? b. How many moles of O 2 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 C 8 H O 2 → 16CO H 2 O

How many moles of octane (C 8 H 18 ) are there in 10.0 gallons (26,714g)?

2 C 8 H O 2 → 16CO H 2 O Use the balanced equation to determine how many moles of CO 2 are produced when all of the octane in the previous question is completely consumed?

When 2.0 mol of octane are burned kj of heat are produced. How many grams of water at 100 degrees Celsius can be boiled?