Name:
Name: Date: Period
Note Taking Guide: Chemical Reactions, Counting Atoms, Writing and Balancing Chemical Equations
What do you know?
▪ What are some signs that a chemical change may be taking place?
▪ What are the reactants of a reaction?
▪ What are the products of a reaction?
▪ Describe the law of conservation of mass.
Demo: Acetic acid (vinegar) and sodium bicarbonate (baking soda) combine to form sodium acetate, water and carbon dioxide gas.
C2H4O2 + NaHCO3 ( NaC2H3O2 + H2O + CO2
Chemical change:
▪ ________________________ is the process by which one or more substances change to produce one or more different substances
▪ Atoms do not become other types of atoms nor do they appear or disappear
o The bonding patterns among the atoms are merely ________________________
▪ Reactants are what you start with or the “original substances”
▪ Products are what you end up with or the “new substances”
▪ Example:
o Camp fire- reactants: wood and fire/match… products: carbon dioxide and water
Evidence of chemical change:
Take 5 minutes and work with a partner to come up with as many examples of evidence that indicate CHEMICAL reactions and chemical change as you can. List them here:
Evidence of chemical change:
|Change in energy |Formation of a new substance |
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Chemical vs Physical change:
▪ Only way to know for sure that an actual chemical reaction has taken place is to do a ________________________on the products
o These test would show that the new substances’ ________________________ such as density, melting point or boiling point are different then the reactants’
Reactions and Energy changes:
▪ Reactions can gain or lose energy
o ________________________: when Energy is released during a reaction it is a ________________________.
▪ Methane + oxygen -> carbon dioxide + water + energy
o ________________________: when Energy is absorbed during a reaction it is a ________________________.
▪ Dinitrogen tetroxide + energy -> nitrogen dioxide
▪ Exothermic reactions yield ________________________
o This is because the bonds holding the products together are stronger than those in the reactants
o The stronger the bond the more energy released when bond forms and more energy to break more bonds in the reactants
Chemical Equation
▪ A representation of a chemical reaction that uses ________________________ to show the relationship between the reactants and the products
▪ Must obey the law of ________________________
▪ Number of atoms on each side of the arrow must be the ____________________
Haber Process
▪ The Haber process is the industrial implementation of the reaction of nitrogen gas and hydrogen gas. It is the main industrial route to ammonia:
▪ N2 + 3 H2 → 2 NH3
Counting Atoms: Why are we doing this?
We need to know how many of each type of atom we have in order to
← Balance Chemical Equations!
Subscripts
_____________________ only refer to the atom that they are _____________________.
For example, in H2S there are TWO atoms of HYDROGEN and only ONE atom of SULFUR.
|H2S |H: |
| |S: |
Coefficients
_____________________ apply to the entire compound. You _____________________ the coefficients and _____________________. If there isn’t a _____________________ behind an element, assume there is only one atom of that element!
For Example:
|2 H2S |H: |
| |S: |
Parenthesis with Polyatomics
If elements or compounds are inside of _____________________, then the _____________________ behind the parentheses applies to everything inside.
|Ba(OH)2 |Ba: |
| |O: |
| |H: |
Let’s practice
|MgCl2 |Mg: |CH3OH |C: |
| |Cl: | |H: |
| | | |O: |
|Al2S3 |Al: |Ca3(PO4)2 |Ca: |
| |S: | |P: |
| | | |O: |
|H2SO4 |H: |Al2(SO4)3 |Al: |
| |S: | |S: |
| |O: | |O: |
Now you do some on your own:
|NaHCO3 | |C6H12O6 | |
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| | | | |
|Mg(OH)2 | |2H2O | |
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| | | | |
|3H3PO4 | |MgO | |
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Challenge:
|2Ca3(PO4)2 | |
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Try a few more!
|NaOH | |4Li2O | |
| | | | |
| | | | |
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|4HNO3 | |2NaOH | |
| | | | |
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|MgCl2 | |Li2SO4 | |
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Day 2: Balancing Equations
• Now that we know how to count the number of atoms
• We can move onto writing and balancing equations!
Writing and balancing a chemical equation
1) _________________ the word equation
2) _________________ the names with molecular formulas. Be sure to leave space in front of each chemical formula
3) _________________ the number of atoms of each element on the left side and compare to the left side. Make a chart if it helps you.
4) _________________in front of appropriate formulas so that the left side has the same number of atoms as the right side for EACH element.
▪ Be careful…sometimes it’s not as easy as it appears.
5) _________________ your answer to ensure a balanced equation.
▪ The numbers of atoms on both sides of the equation must be equal.
▪ The coefficients for each reactant & product must be in the _________________ possible whole number ratio. If they are not, divide the coefficients by their greatest common factor to obtain the smallest possible whole-number coefficients.
A few balancing tips
1) Delay the balancing of elements (often H and O) that occur in several reactants or products
2) If the same polyatomic ions appear on both sides of the equation, treat them as single units, like monatomic ions
3) After using steps 1&2, balance the elements left to right
4) Remember, balancing one element may unbalance others (So ALWAYS double check at the end!!!)
5) For ionic equations, be sure charges are balanced (If/when we use these)
Stop: Complete balancing worksheet
Let’s try balancing some
a) Balance the equation for the reaction of iron (III) oxide with hydrogen to form iron and water.
Word: iron (III) oxide + hydrogen (diatomic) ( iron + water
Formula: ___Fe2O3 + ___H2 -> ___Fe + ___H2O
b) The reaction of ammonia with oxygen produces nitrogen monoxide and water vapor. Write the balanced equation for this reaction.
Word: ammonia + oxygen (diatomic) ( nitrogen monoxide + water
Formula: ___NH3 + ___O2 -> ___NO + ___H2O
Let’s add in writing the formulas!
c) Methane reacts with oxygen to form carbon dioxide and water
Word: ________________________________________________
Formula: ________________________________________________
d) Mercury and oxygen react to form mercury (II) oxide.
Word: ________________________________________________
Formula: ________________________________________________
(e) Iron reacts in air to form rust otherwise known as iron (III) oxide
Word: ________________________________________________
Formula: ________________________________________________
(f) Potassium chlorate decomposes into potassium chloride and oxygen.
Word: ________________________________________________
Formula: ________________________________________________
(g) Copper metal placed in a silver nitrate solution will react to form copper (II) nitrate and silver metal.
Word: ________________________________________________
Formula: ________________________________________________
Important Information!
▪ Chemical equations tell more than just what is used and made in a reaction
▪ Shows how much of everything is in a reaction
▪ Tells temperature and/or pressure needed for the reaction
State symbols and Reaction conditions
▪ The physical states of the reactants and products are provided in the equation.
| (g) | |(l) | |
|(s) | |(aq) | |
(aq) = aqueous, which means “mixed with water” (for a substance dissolved in water)
▪ If special conditions are necessary for a reaction to take place, they are often specified above the arrow.
▪ Some examples of special conditions are electric current, high temperature, high pressure, or light.
Never ever ever…
▪ DO NOT CHANGE SUBSCRIPTS
▪ If you change these you are changing the compounds in the reactions!!!
▪ We can only change the coefficients to make the number of atoms balance
o When we change these we are just changing the number of moles of the substance needed in the reaction
What about polyatomics?
▪ Sometimes a polyatomic ion will stay intact throughout the reaction so when we go to balance the equation we can think of it as its own “atom”
Let’s try some:
(a) ___Al + ___H2(SO4) -> ___Al2(SO4)3 + ___H2
(b) ___Al + ___H(AsO3) -> ___H2 + ___Al (AsO3)3
(c) ___Mg(NO3)2 + ___Cu ( ___ CuNO3 + ___ Mg
-----------------------
|N - |N - |
|O - |O - |
|H - |H - |
|Fe - |Fe - |
|O - |O - |
|H - |H - |
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