January 17, 2014
Unit 4: Chemical Reactions
What is a chemical reaction? • the process by which the atoms of one or more substances are rearranged to form different substances • chemical change
What chemical reactions are important in your life? January 17, 2014
Evidence of Chemical Reaction (or chemical change)
1. Temperature change 2. Light 3. Color change 4. Production of gasses 5. Production of solids (precipitate) 6. Odor change
What evidence of a chemical reaction do you see in a fire?
What evidence of a chemical reaction do you see when you roast a marshmallow? January 17, 2014
Representing Chemical Reactions
As chemists, we can describe chemical reactions in different ways. 1. In a sentence 2. Word equations 3. Skeleton equation 4. Chemical equations
Reactants are the starting substances of a reaction. Products are the substances formed during the reaction.
reactant 1 + reactant 2 product 1 + product 2
This arrow separates the reactants from the products When you have more (kind of like the equal sign in than one reactant or math) product, use a plus sign January 17, 2014
1. In a sentence "Solid iron and chlorine gas react to produce solid iron (III) chloride."
2. Word Equation
iron(s) + chlorine(g) iron (III) chloride(s)
The letters in parentheses shows you the state of matter: (s) = solid state (l) = liquid state (g) = gas state (aq) = water solution
3. Skeleton Equation: uses chemical formulas
Fe(s) + Cl2(g) FeCl3(s) January 17, 2014
Examples
Write skeleton equations for these word equations.
1. hydrogen(g) + bromine(g) hydrogen bromide(g)
2. carbon monoxide(g) + oxygen(g) carbon dioxide(g)
3. potassium chlorate(s) potassium chloride(s) + oxygen(g) January 17, 2014
Write the word equation and describe in a sentence the following reactions:
1. Mg(s) + FeCl3(aq) Fe(s) + MgCl2(aq)
2. Ba(s) + O2(g) BaO(s)
3. Fe(s) + H2SO4(aq) Fe2(SO4)3(aq) + H2(g) January 17, 2014
4. Chemical equation: Balanced equation that shows the reactants and products, and the relative amounts involved in the reaction. • Conservation of mass • Need to have same # of atoms of each element in the reactants and products.
skeleton equation: Fe(s) + Cl2(g) FeCl3(s)
chemical equation: 2Fe(s) + 3Cl2(g) 2FeCl3(s) January 17, 2014
How to balance chemical equations 1. Write the skeleton equation. 2. Count the atoms of the elements in the reactants and products. 3. Use coefficients to make the # of atoms of each element equal on both sides of the equation. • coefficients = numbers written in front of a reactant or product. Tells us the number of particles of the substance involved in the reaction.
skeleton equation: Fe(s) + Cl2(g) FeCl3(s)
chemical equation: January 17, 2014
How to balance chemical equations 1. Write the skeleton equation. 2. Count the atoms of the elements in the reactants and products. 3. Use coefficients to make the # of atoms of each element equal on both sides of the equation. 4. Make sure coefficients are in their lowest possible ratio. 5. Check your work! January 17, 2014
Practice Problems: Write the balanced chemical equation for each. 1. Hydrogen gas and chlorine gas combine to form hydrochloric acid (HCl)
2. CS2(l) + O2(g) CO2(g) + SO2(g) January 17, 2014
More practice balancing equations!
1. CaO(s) + H2O(l) Ca(OH)2(s)
2. NaOH(aq) + CaBr2(aq) Ca(OH)2(s) + NaBr(aq) January 17, 2014
Classifying Chemical Reactions
Types of chemical reactions: 1. Synthesis 2. Decomposition 3. Combustion 4. Single-Replacement 5. Double-replacement
*Classifying how atoms rearrange during a chemical reaction January 17, 2014
1. Synthesis reaction: 2 or more substances react to produce a single product
A + B AB
Ex:
2Na(s) + Cl2(g) 2NaCl(s)
CaO(s) + H2O(l) Ca(OH)2(s) January 17, 2014
2.Decomposition Reaction: A single compound breaks down into two or more substances. (opposite of synthesis)
AB A + B
Ex:
NH4NO3(s) N2O(g) + 2H2O(g)
Car air bags!: 2NaN3(s) 2Na(s) + 3N2(g) January 17, 2014
3. Combustion reaction: Oxygen combines with a substance and releases energy in the form of heat and light.
Always need O2!
Ex:
2H2(g) + O2(g) 2H2O(g)
C(s) + O2(g) CO2(g) January 17, 2014
Practice: Classify each of the following reactions
1. CH4(g) + 2O2(g) CO2(g) + 2H2O(g)
2. 2Al(s) + 3S(s) Al2S3 (s)
3. H2O(l) + N2O5(g) 2HNO3(aq)
4. Ni(OH)2(s) NiO(s) + H2O(l) January 17, 2014
4. Single Replacement Reaction: A reaction in which the atoms of one element replaces the atoms of another element in a compound.
A + BX AX + B
Ex:
2Li(s) + 2H2O 2LiOH(aq) + H2(g)
Cu(s) + 2AgNO3 January 17, 2014 January 17, 2014
Use activity series to predict whether or not certain reactions will happen. January 17, 2014
Predict whether or not this reaction will occur:
Ag(s) + Cu(NO3)2(aq)
F2(g) + 2NaBr(aq) January 17, 2014
5. Double Replacement Reaction: Reaction in which there is an exchange of ions between compounds.
AX + BY AY + BX
*Cations switch places *Always produce a precipitate, a gas, or water
Ex: Ca(OH)2(aq) + 2HCl(aq) CaCl2(aq) + 2H2O(aq)
KCN(aq) + HBr(aq) January 17, 2014
Practice classifying these reactions. There may be more than one classification for each!
1. 3Ni + 2AuBr2 3NiBr2 + 2Au
2. 2HI(g) H2(g) + I2(g)
3. FeO(s) + O2(g) Fe2O3(s)
4. Fe(s) + Sn(NO3)4 (aq) Fe(NO3)3 + Sn(s)
5. LiCrO4(aq) + BaCl2(aq) LiCl(aq) + Ba(CrO4)2(s) January 17, 2014