Chemical Equations and Reactions What are they?

The Two Sides of a Chemical Reaction Na + Cl  NaCl Definition: A chemical change – one or more substances are changed into new substances. The Two Sides of a Chemical Reaction Reactant – About to be changed Product – The new substance

Symbol for Chemical Equations Pb(NO3)2 + 2KI  PbI2 + 2KNO3 “Pb(NO3)2” is a formula.  Means produces (or yields) + Means added together Coefficients – Number of molecules Subscripts - Number of a particular atom in a molecule

Father of modern chemistry 1743 - 1794 Antoine Lavoisier First Described the “Law of Conservation of Matter”

Conservation of mass HgO Hg + O2 Antoine Lavoisier found that the mass of the reactants and the products are equal, even when the states of matter change. 0.7g Oxygen became a gas HgO Hg + O2 He started with: 10g of Mercury Oxide (HgO) He ended up with: and 9.3g Mercury… ...But what happened to the O2? 10 g. = 0.7 + 9.3 g. This is the Law of the Conservation of Matter – Matter is neither created or destroyed

Hg (mercury) can exist by itself... This Balances the equation! Lavoisier’s chemical equation: 2 HgO  2 Hg + O2 Hg (mercury) can exist by itself... but, Oxygen will need to bond with another oxygen to make O2 To balance the atoms we need to: Put the coefficient of 2 in front of reactant HgO Put the coefficient of 2 in front the product Hg This Balances the equation!

Easy, Right? Not that easy? Let’s try...

VISUALIZING to balance an Equation…

Equations must be balanced H2 O H2 + O2 Law of Conservation of Mass

Equations must be balanced 2 H2 O 2 H2 + O2 Matter is neither created or destroyed

N2 H2 NH3 Why or Why Not? Is this reaction possible? 11 Is this reaction possible? N2 H2 NH3 Why or Why Not? Let’s Count the Atoms: N H N H There are 2 nitrogen atoms There are 2 hydrogen atoms 1 nitrogen and 3 hydrogen…

Before we get balancing let’s look at a couple of rules.

Atoms can only bond in certain ways.. H2 N2 N H2 H N2 H N H H2 H2 H N That’s why we can’t change the subscripts. N2 H2 H N N2 N N2 N H

I can’t live without you! Here is what it means... Subscripts - Small #’s below an element. Coefficients - Large #’s in front of the formulas. H2 2H2 H H I can’t live without you! H When balancing equations we can only change the Coefficients!

1 N2 1 H2 1 NH3 We can only change coefficients before the symbols 15 Now, back to the balancing... 1 N2 1 H2 1 NH3 We can only change coefficients before the symbols N H N H 1 molecule of nitrogen 1 molecule of hydrogen 1 molecule of ammonia

There are too many nitrogen atoms and not enough hydrogen atoms After counting the atoms we know... N H N H There are too many nitrogen atoms and not enough hydrogen atoms

A little common sense math goes a long way in making this equation balance… There are 2 nitrogen atoms. We will 2 more molecules for a total of 6 hydrogen atoms. That will make 2 NH3 N H H N H H N H Count the atoms. Is it balanced?

Then it’s a balanced equation Do both sides have the same amount of Atoms? N H H N H H N H N2 + 3 H2 2NH3 Then it’s a balanced equation

Four Steps to Balance Equations: 1. Set up your equation Write the metals, nonmetals, oxygen, and hydrogen. 2. Count and then write the number of atoms you have on both sides. 3. Balance by changing the coefficients and recounting. 4. Start the process again if it still does not balance.

H2 + O2  H2O O H 1. Set up your equation Write the elements in this order: Metals, Nonmetals, Oxygen, Hydrogen H2 + O2  H2O O H

2. Count and write the number of atoms you have of each on both sides. H2 + O2  H2O 2 O 1 2 H 2

3. Balance by changing the coefficients and recounting. 2 2 H2 + O2  H2O O H 2 1 (2) Need to have at least 2 “O” (4) (4) But it changes the number of “H” How are you going to make “H” add up to 4? Is this balanced? Yes!

Need to have at least 2 “Cl” Changing the Cl changes the “H”? Let’s try another: 2 Mg + HCl  H2 + MgCl2 1 Mg 1 (2) 1 Cl 2 Need to have at least 2 “Cl” Is this balanced? Yes! 2 Changing the Cl changes the “H”? (2) 1 H

Na + HCl  NaCl + H2 Na Cl H 1 2 2 (2) Let’s try another: In this case, we will start with hydrogen since it is the only one unbalanced. (2)

Na + HCl  NaCl + H2 Na Cl H 1 2 (2) (2) But, changing the Hydrogen in HCl effects the number of chlorine atoms. So you must change number on both sides to reflect the change. Na + HCl  NaCl + H2 Na Cl H 1 2 (2) (2)

Na + 2HCl  NaCl + H2 Na Cl H 1 2 (2) 2 (2) But, changing the Hydrogen in HCl effects the number of chlorine atoms. So you must change the number on both sides to reflect the change. Na + 2HCl  NaCl + H2 Na Cl H 1 2 (2) 2 (2)

Na + 2HCl  NaCl + H2 2 (2) 1 Na (2) Cl (2) H 2 Changing the chlorine on the product side effects the sodium (Na) on the reactants side. So we must now change it as well. Na + 2HCl  NaCl + H2 Na Cl H 1 2 (2) 2 (2) (2)

http://www.wfu.edu/~ylwong/balanceeq/balanceq.html http://www.chem.vt.edu/RVGS/ACT/notes/scripts/bal_eq1.html

4 Types of Chemical Reactions Synthesis Decomposition Single Displacement Double Displacement

Two or more substances combine to form a new one Synthesis A + B  AB 2H2 + O2  2H2O Two or more substances combine to form a new one

AB  A + B 2MgO  2Mg + O2 Decomposition The opposite of synthesis; substance breaks down into 2 or more simpler substances

A + BC  AC + B Zn + Cu(NO3)2  Zn(NO3)2 + Cu Single Displacement Occurs when one element replaces another in a compound; a zinc strip is put into copper nitrate solution and the copper precipitates out (it turns solid)

Occurs when two element “switches” with one another compound; Double Displacement AB + CD  AD + CB HCl + NaOH  HOH + NaCl (H2O) Occurs when two element “switches” with one another compound;