Chapter 8 CHEMICAL REACTIONS

COMPONENTS OF A CHEMICAL REACTION ReactantsCatalystProduct(s) MnO 2 Fe(s) +O 2 (g)Fe 2 O 3 (s) State designations (s=solid, g=gas, l=-liquid, aq=aqueous) Arrow separates reactants from products

 A skeleton equation is one that may not be balanced. If good formulas are written and the equation is balanced, you are done!  All formulas and states are written correctly.  A catalyst is a substance that speeds up a reaction but is not used in the reaction.

BALANCING CHEMICAL EQUATIONS  In a balanced equation, the number and types of atoms on the reactant side must equal the number and types of atoms on the product side.

Rules for balancing 1.Determine correct formulas. 2.Write reactant formulas left of arrow and product formulas right of arrow. 3.Count the number of atoms of each element on each side of the equation (polyatomic ions can be counted as a single unit if they appear on both sides of the equation.)

4.Balance using coefficients. Coefficients may only be placed in front of a formula! 5.Check for conservation of mass 6.Make sure coefficients are in the lowest whole number ratio.

SYNTHESIS REACTIONS  Also called combination reactions  General format:A + B C  When a nonmetal oxide reacts with water, an acid is produced.  An acid is generally hydrogen bonded with a nonmetal or polyatomic ion.  SO 2 (g) + H 2 O(l)H 2 SO 3 (aq)  Nonmetal oxide + wateracid

SYNTHESIS REACTIONS  When a metal oxide reacts with water, a base is produced.  A base consists of a metal and a(n) hydroxide ion.  CaO(s)+H 2 O(l)Ca(OH) 2 Metal oxidewaterbase

DECOMPOSITION REACTIONS  General format:A B + C  Difficult to predict products unless the decomposing compound is binary.  Usually requires energy to proceed.

DECOMPOSITION REACTIONS  Metal hydrogen carbonates are a special type of decomposition reaction.  A metal hydrogen carbonate undergoes decomposition when heated.  Format: metal hydrogen carbonate Metal carbonate + H 2 O + CO 2

DECOMPOSITION REACTIONS  Metal carbonates can further decompose with prolonged heating.  General format:  metal carbonate metal oxide +CO 2

SINGLE REPLACEMENT REACTIONS  General format: A + BX B + AX (Metal switches) or Y + AX X + AY (Halogen switches)  Whether a RXN will proceed depends on the activity of the metals or halogens involved.  The activity series of metals and of halogens is used to determine whether a RXN will proceed.  A RXN will proceed if the elemental reactant is higher in the series than the combined metal (or halogen)

DOUBLE REPLACEMENT REACTIONS  Involves the exchange of ions between two compounds.  General format: AX + BY AY + BX These reactions usually take place when two ionic compounds are in aqueous solution

DOUBLE REPLACEMENT REACTIONS  For a double replacement reaction to occur one of the following is usually true: One product is only slightly soluble and precipitates from solution. (a precipitate is a solid that is formed during a reaction of aqueous solutions) One product is a gas that bubbles out of the mixture. One product is a molecular compound such as water.

NEUTRALIZATION REACTIONS  An acid (HX) reacts with a base (BOH) to form an ionic compound and water.  General format: HX + BOH BX + HOH  Special type of double replacement reaction

COMBUSTION REACTIONS  A fuel reacts with oxygen to form water and carbon dioxide.  General format: fuel + O 2 CO 2 + H 2 O  These are sometimes difficult to balance.  Oxygen, carbon dioxide and water are always located as described in the general format.

NET IONIC EQUATIONS  Once you have written and balanced a single or double replacement reaction, you may separate the ionic compounds into their constituent ions.  All aqueous solutions dissociate and must be separated  The resulting equation is called the complete ionic equation

NET IONIC EQUATIONS  Ions that appear exactly the same on each side of the equation are called spectator ions.  Spectator ions may be eliminated and the equation rewritten to obtain the net ionic equation.

NET IONIC EQUATIONS  Complete, balanced equation: AgNO 3 (aq) + NaCl(aq)AgCl(s) + NaNO 3 (aq)

NET IONIC EQUATIONS  Dissociate all aqueous substances for complete ionic equation. Do not dissociate the solid! Ag + (aq)+ NO 3 - (aq) + Na + (aq) + Cl - (aq) AgCl(s) + Na + (aq) + NO 3 - (aq)

NET IONIC EQUATIONS  Cross out the spectator ions to get the net ionic equation Ag + (aq)+ NO 3 - (aq) + Na + (aq) + Cl - (aq) AgCl(s) + Na + (aq) + NO 3 - (aq) Ag + (aq) + Cl - (aq) AgCl(s)

Balancing the EASY way 1.Pick the largest compound 2.Place a 1 in front. 3.Pick one of the elements (two places not three) 4.Balance that element 5.Repeat If you are unable to balance one element, place a 2 in front of the starting compound and repeat.