Chemical Reactions
Chemical Reaction Types There are 5 types of chemical reactions that you need to know Combination reaction Decomposition reaction Combustion reaction Single replacement (redox) reaction Double replacement reaction
Summary Chemical Reactions Combination: A + X AX Decomposition: AX A + X Combustion: C X H Y O Z + O 2 H 2 O + CO 2 Single replacement: A + BX B + AX Double replacement: AX + BY AY + BX
Combination Reaction A combination reaction is one in which two or more substances combine to form a single product Also known as a synthesis reaction General equation: A + X AX Example: 2Na(s) + Cl 2 2NaCl(s)
Combination Reaction Write the equation for the formation of solid sodium peroxide (Na 2 O 2 ) by direct combination of solid sodium and oxygen gas. Notice that this is a combination reaction Na (s) + O 2(g) Na 2 O 2(s) Now we need to balance the equation
Combination Reaction Na(s) + O 2 (g) Na 2 O 2 (s) Na = 1 Na = 2 O = 2 O = 2 Balance the Na atoms by placing a 2 in front of Na 2Na(s) + O 2 (g) Na 2 O 2 (s) Na = 2 Na = 2 O = 2 O = 2 This reaction is completely balanced!
Combination Reactions Now you try one! Carbon dioxide gas is formed when charcoal (solid carbon) is burned with oxygen in the air. Write the chemical equation.
Combination Reactions Carbon dioxide gas is formed when charcoal (solid carbon) is burned with oxygen in the air. Write the chemical equation. C (s) + O 2(g) CO 2(g) Now balance the equation This equation is already balanced!
Decomposition Reactions A decomposition reaction is the opposite of a combination reaction One compound breaks down into simpler substances Products can be elements or compounds General equation: AX A + X Example: 2HgO (s) 2Hg + O 2(g)
Decomposition Reactions A common lab procedure for producing oxygen gas is to heat solid potassium chlorate. Solid potassium chloride is left behind. Write the equation. KClO 3(s) O 2(g) + KCl (s) Now balance the equation! 2KClO 3 (s) 3O 2 (g) + 2KCl(s)
Combustion Reactions Combustion Reactions also called burning reactions In a combustion reaction, there are two reactants One reactant contains carbon and hydrogen (and sometimes oxygen) The other reactant is always O2(g) In a combustion reaction, the products are ALWAYS THE SAME CO 2(g) and H 2 O
Combustion Reactions For combustion reactions you will only be given one reactant and will have to write the equation Remember The other reactant is ALWAYS O 2 (g) The products are ALWAYS CO 2 (g) + H 2 O(l or g) Combustion, oxidized, or burned will clue you in that it s a combustion reaction
Combustion Reactions General equation Example: C X H Y O Z + O 2(g) CO 2(g) + H 2 O (g or l) CH 4(g) + O 2(g ) CO 2(g) + H 2 O (g) Now balance the equation In combustion reactions, it s easiest if you balance C first, then H, and O last CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g)
Combustion Reactions Write the equation for the combustion of ethane, C 2 H 6 (g) C 2 H 6 (g) + O 2 (g) CO 2 (g) + H 2 O(g) Now balance the equation (this one is a little trickier) Start with the C, then H, then O
Combustion Reactions C 2 H 6(g) + O 2(g CO 2(g) + H 2 O (g) C = 2 C = 1 H = 6 H = 2 O = 2 O = 3 First, let s balance the C atoms by putting a 2 in front of CO 2
Combustion Reactions C 2 H 6(g) + O 2(g 2CO 2(g) + H 2 O (g) C = 2 C = 2 H = 6 H = 2 O = 2 O = 5 Now let s balance the H atoms by putting a 3 in front of H 2 O
Combustion Reactions C 2 H 6(g) + O 2(g 2CO 2(g) + 3H 2 O (g) C = 2 C = 2 H = 6 H = 6 O = 2 O = 7 Now let s balance the O atoms. Put a 7/2 fraction in front of O 2.
Combustion Reactions C 2 H 6(g) + 7/2O 2(g 2CO 2(g) + 3H 2 O (g) C = 2 C = 2 H = 6 H = 6 O = 2 (7/2) O = 7 Now the reaction is balanced, but we have to remove the fraction by multiplying everything by the denominator in this case 2
Combustion Reactions 2C 2 H 6(g) + 7O 2(g 4CO 2(g) + 6H 2 O (g) C = 4 C = 4 H = 12 H = 12 O = 14 O = 14 Now the reaction is completely balanced!
Combustion Reactions Write the equation for the complete burning of butanol, (butyl alcohol) C 4 H 9 OH (l)
Combustion Reactions Write the equation for the complete burning of butanol, C 4 H 9 OH (l) C 4 H 9 OH (l) + O 2(g) CO 2(g) + H 2 O (g) Now we need to balance the equation C 4 H 9 OH (l) + 6O 2(g) 4CO 2(g) + 5H 2 O (g)
Single Replacement Reactions Single replacement reactions are also called a redox reaction One element replaces another element in a compound Reactants are always one element and one compound General equation: Example: A + BX AX + B Zn (s) + Pb(NO 3 ) 2(aq) Zn(NO 3 ) 2(aq) + Pb (s)
Single Replacement Reactions Write a single replacement reaction between solid elemental calcium and hydrochloric acid Ca (s) + HCl (aq) CaCl 2(aq) + H 2(g) Ca and H form cations, so the only thing that Ca can bind to is Cl (which forms an anion)
Note: when combining atoms you need to pay attention to the charges of the ions and make certain that the ionic compound you create has the right formula based on charge Example: when combining Ca and Cl in the previous example, first find the charges you would expect each ion to have by finding their location on the Periodic Table
Ca is in group 2A and so has a charge of 2+ Cl is in group 7A and so has a charge of 1- If we criss-cross the charges they will become the subscripts for the correct formula of the compound Of course, we never show a subscript of 1, and we never include signs as part of the subscript so the final formula looks like CaCl 2 Ca 2+ Cl 1- Ca 1 Cl 2
Remember too, when H is no longer part of a compound it will always be shown as a Diatomic Element: H 2 Once you have the correct formulas for the products, then you can begin to balance the chemical equation
Single Replacement Reactions Ca (s) + HCl (aq) CaCl 2(aq) + H 2(g) Now balance the equation Ca (s) + 2HCl (aq) CaCl 2(aq) + H 2(g)
Single Replacement Reactions Copper reacts with a solution of silver nitrate Write the equation
Again, you need to determine the charges on the atoms or polyatomic ion that will combine in this reaction: Cu (s) + AgNO 3(aq) Cu and NO 3 combine to give what product?
Add the charges you expect each to have Now criss-cross Cu 2+ NO 3 1- to get your subscripts Cu 1 NO 3 2 But cannot show subscript of 1 and for polyatomic ions you must use parentheses is you are going to have a subscript of 2 or more Correct formula: Cu(NO 3 ) 2
When Cu kicks the Ag out and replaces it Ag is the other product Ag is not one of the Diatomic Elements so Ag can just be written as is
Single Replacement Reactions Copper reacts with a solution of silver nitrate. Write the equation. Cu (s) + AgNO 3(aq) Cu(NO 3 ) 2 + Ag (s) Now balance the equation Cu (s) + 2AgNO 3(aq) Cu(NO 3 ) 2 + 2Ag (s)
Double Replacement Reactions In a double replacement reaction, solutions of 2 compounds are mixed A cation from one compound may combine with the anion from the other compound (the ions change partners) General equation: Example: AX + BY AY + BX CaCl 2 (aq) + 2NaF(aq) CaF 2 (s) + 2NaCl(aq)
Double Replacement Reactions When this happens, one of three things will occur The formation of a solid The formation of a gas The formation of water These represent the 3 types of double replacement reactions that you need to know Double-replacement precipitation reaction Double-replacement gas-forming reaction Double-replacement neutralization
Double Replacement Reactions Precipitation When a precipitation reaction occurs, a solid forms from the mixing of 2 aqueous solutions There will be another aqueous product as well
Double Replacement Reactions Precipitation Solid barium chromate forms when solutions of potassium chromate and barium nitrate are mixed. Write the equation. K 2 CrO 4 (aq) + Ba(NO 3 ) 2 (aq) What combines with what? K combines with NO 3 and Ba combines with CrO 4 Remember the cation always comes first in the final product formula!
Double Replacement Reactions Precipitation Use charges to create correct product formulas K 1+ NO 3 1- Ba 2+ CrO 4 2- Remember, if the charges are the same size just put the atoms together to create the formula KNO 3 and BaCrO 4 No parentheses needed for polyatomic ions if there is only one in the formula
Double Replacement Reactions Precipitation Solid barium chromate forms when solutions of potassium chromate and barium nitrate are mixed. Write the equation using the formulas you created as your products: K 2 CrO 4(aq) + Ba(NO 3 ) 2(aq) BaCrO 4(s) + KNO 3(aq) Now balance the equation K 2 CrO 4(aq) + Ba(NO 3 ) 2(aq) BaCrO 4(s) + 2KNO 3(aq)
Double Replacement Reactions Precipitation Silver chloride precipitates when solutions of sodium chloride and silver nitrate are combined. Write the equation for this reaction.
Double Replacement Reactions Precipitation Silver chloride precipitates when solutions of sodium chloride and silver nitrate are combined. Write the equation for this reaction. NaCl (aq) + AgNO 3(aq) AgCl (s) + NaNO 3(aq) Now we need to balance it This equation is already balanced!
Double Replacement Reactions Neutralization Neutralization reactions result from the mixing of an acid and a base Acid: releases H + Base: contains hydroxide ions (OH - ) H + combine with OH - to form H 2 O The products are always water and ionic compound called a salt
Double Replacement Reactions Neutralization General equation: HX (aq) + MOH (aq or s) MX (aq) + H 2 O (l) M = metal cation Hint: to balance the equation, start with the ions in the salt!
Double Replacement Reactions Neutralization Write the equation for the reaction between sulfuric acid and solid aluminum hydroxide. H 2 SO 4(aq) + Al(OH) 3(s) H 2 O (l) + Al 2 (SO 4 ) 3(aq) Now balance this equation (remember, start with the ions in the salt first!) 3H 2 SO 4(aq) + 2Al(OH) 3(s) 6H 2 O (l) + Al 2 (SO 4 ) 3(aq)
Double Replacement Reactions Neutralization Write the equation for the reaction between: aqueous phosphoric acid and solid magnesium hydroxide
Double Replacement Reactions Neutralization Write the double replacement neutralization equation for the reaction between aqueous phosphoric acid and solid magnesium hydroxide H 3 PO 4(aq) + Mg(OH) 2(s) H 2 O (l) + Mg 3 (PO4) 2(s) Now balance this equation 2H 3 PO 4(aq) +3Mg(OH) 2(s) 6H 2 O (l) + Mg 3 (PO4) 2(s)
Summary Chemical Reactions Combination: A + X AX Decomposition: AX A + X Combustion: C X H Y O Z + O 2 H 2 O + CO 2 Single replacement: A + BX B + AX Double replacement: AX + BY AY + BX
Chemical Reactions