Chemical Reactions GPS 10

Indicators of a chemical reaction: 1.Precipitation of a Solid 2.A distinct color change 3.Formation of a gas (bubbling or fizzing) 4.Combustion of a substance (fire usually involved)

Types of Chemical Reactions Synthesis Two or more substances react to form a single new substance General reaction: Example:2H 2 + O 2 → 2H 2 O

Types of Chemical Reactions Decomposition A single substance breaks down into two or more substances General reaction: Example:2Ag 2 O → 4Ag + O 2

Types of Chemical Reactions Single Replacement Atoms of one element replace atoms of another element in a compound General reaction: Example:Cl 2 + 2KBr → 2KCl + Br 2

Types of Chemical Reactions Double Replacement Ions are exchanged between two compounds General reaction: Example:PbCl 2 + Li 2 SO 4 → PbSO 4 + 2LiCl

Types of Chemical Reactions Combustion A special type of synthesis reaction in which a hydrocarbon reacts with oxygen, producing carbon dioxide and water General reaction: C x H y + O 2 → CO 2 + H 2 O Example:

Types of Chemical Reactions Neutralization A special type of double replacement reaction in which an acid reacts with a base to produce a salt and water General reaction: HX + YOH → YX + H 2 O Example: Acids begin with “H”Many bases contain “OH” *Reactants are solutions containing dissolved ions of Na +, OH -, H +, Cl - *Product is a solution of salt water, with dissolved ions of Na + and Cl - surrounded by water molecules

Types of Chemical Reactions Cl 2 + KBr → KCl + Br 2 H 2 + O 2 → H 2 O PbCl 2 + Li 2 SO 4 → PbSO 4 + LiCl Ag 2 O → Ag + O 2 H 2 S + Mg(OH) 2 → MgS + H 2 O CH 4 + O 2 → CO 2 + H 2 O

Redox reactions Reduction-oxidation reactions (REDOX) –a chemical reaction that involves the transfer of electrons –atoms involved in the reaction change oxidation numbers (charges) Redox reactions include: –Single replacement reactions –Decomposition reactions –Synthesis reactions

Balancing Equations H 2 + O 2 → H 2 O What’s wrong with this reaction? HINT: Recall that the Law of Conservation of Matter states that matter cannot be created or destroyed

Balancing Equations Coefficients Numbers placed in front of a substance in order to balance chemical equations Example:2 H 2 + O 2 → 2 H 2 O

Balancing Equations Steps to balancing equations: 1. Write reactants on the left of the reaction arrow, products on the right 2. Balance each element one at a time using coefficients (hint, leave H and O for last) 3. Reduce any coefficients if possible 4. Double check that the same number of each atom are on each side of the equation

Balancing Equations H 2 + O 2 → H 2 O Ag 2 O → Ag + O 2 Cl 2 + KBr → KCl + Br 2 PbCl 2 + Li 2 SO 4 → PbSO 4 + LiCl CH 4 + O 2 → CO 2 + H 2 O H 2 S + Mg(OH) 2 → MgS + H 2 O

The State of Substances Symbols are used to tell you what state a substance is in: (s) = substance is a solid (g) = substance is a gas (l) = substance is a liquid (aq) = substance is aqueous (aqueous means it’s dissolved in water) Example: 2Ag 2 O (s) → 4Ag (s) + O 2 (g)

Predicting Chemical Reactions Example: Solid calcium reacts with oxygen gas to produce a solid. What type of reaction is taking place? Write the balanced equation for this reaction.

Predicting Chemical Reactions Example: Dinitrogen pentachloride decomposes. What type of reaction is taking place? Write the balanced equation for this reaction.

Predicting Chemical Reactions Example: Methane reacts with oxygen gas. What type of reaction is taking place? Write the balanced equation for this reaction.

Predicting Chemical Reactions When a solution is aqueous (aq), it means it is dissolved in water You must use solubility rules to determine which substances dissolve and which substances remain solid The following are aqueous reactions: –Double replacement –Neutralization (a type of double replacement) –Single replacement

Solubility Rules All nitrates (NO 3 - ) are soluble (dissolve) All alkali metal salts (Na +, K +, etc.) and ammonium (NH 4 + ) salts are soluble All halogen salts (Cl -, Br -, etc.) are soluble EXCEPT when they contain silver (Ag), mercury (Hg), or lead (Pb)

Predicting Chemical Reactions Example: Solid lead (II) carbonate reacts with aqueous potassium hydroxide. What type of reaction is taking place? Write the balanced equation, write the full ionic equation, and write the net ionic equation for this reaction. The product containing lead is a solid.

Precipitation Reactions Example A yellow solution of potassium chromate (K 2 CrO 4 ) is added to a colorless solution of barium nitrate (Ba(NO 3 ) 2 ). A yellow precipitate forms. What is the precipitate? Write the complete balanced equation, the full ionic equation, and the net ionic equation for this reaction.

Precipitation Reactions Example A solution of sliver nitrate (AgNO 3 ) is added to a solution of potassium chloride (KCl). Will a precipitate form? If so, what is the precipitate? Write the complete balanced equation, the full ionic equation, and the net ionic equation for this reaction.

Precipitation Reactions Examples For each of the following, predict if a precipitate will form. If so, write the net ionic equation for the reaction. 1. KNO 3(aq) and BaCl 2(aq) 2. Na 2 SO 4(aq) and Pb(NO 3 ) 2(aq) (product containing lead is a solid) 3. KOH (aq) and Ba(NO 3 ) 2(aq) (product containing barium is a solid)

Single Replacement Reactions Examples Chlorine gas is bubbled through a solution of silver (I) nitrate. Write the complete balanced equation, the full ionic equation, and the net ionic equation for this reaction.

Single Replacement Reactions Examples Solid zinc(II) reacts with a solution of hydrochloric acid (HCl). The product containing Zn is a solid. Write the complete balanced equation, the full ionic equation, and the net ionic equation for this reaction.

Neutralization Reactions Solubility of Acids and Bases: If the acid (or base) is strong it completely dissociates into ions - It will appear as ions on both sides of your equation If the acid (or base) is weak it does NOT completely dissociate into ions - It will appear as a compound on the left (reactants) side and as ions on the right (products) side to represent partial dissociation

Strength vs. Concentration The strength of an acid or base is NOT dependent on its concentration. Weak acids and bases do NOT dissociate completely Strong acids and bases dissociate (break into ions) completely

Strong Acids and Bases Strong Acids: hydrochloric (HCl), hydrobromic (HBr), hydroiodic (HI), nitric (HNO 3 ), perchloric (HClO 4 ), sulfuric (H 2 SO 4 ) Strong Bases: Alkali metal hydroxides (LiOH, NaOH, KOH, RbOH, CsOH) Alkaline earth metal hydroxides (BaOH 2, CaOH 2, SrOH 2 ) when solutions have a concentration of 0.01M or less

Acid-Base Reactions Example: What is the net ionic equation for the reaction of HCl (aq) and KOH (aq) ?

Acid-Base Reactions Example: What is the net ionic equation for the reaction of Fe(OH) 2 (aq) and HI (aq) ?

Acid-Base Reactions Example: What is the net ionic equation for the reaction of HC 2 H 3 O 2(aq) and KOH (aq) ?

Using the Law of Conservation of Matter Recall: –the Law of Conservation of Matter states that matter cannot be created or destroyed Use this law to balance equations –Example: 2H 2 + O 2 → 2H 2 O 8.9 g2.1 g? 11.0 g of water produced

Using the Law of Conservation of Matter How much chlorine gas is needed? Ca + Cl 2 → CaCl g65.4 g?

Redox reactions Reduction-oxidation reactions (REDOX) –a chemical reaction that involves the transfer of electrons –atoms involved in the reaction change oxidation numbers (charges) Redox reactions include: –Single replacement reactions –Decomposition reactions –Synthesis reactions

Redox reactions Example: Cl 2(g) + HBr (aq) → HCl (aq) + Br 2(l) - any pure substance (diatomic molecules and metals) have oxidation number = zero

Redox reactions Example: Determine if this is a redox reaction. AgNO 3(aq) + Cu (s) → Cu(NO 3 ) 2(aq) + Ag (s)

Redox reactions Oxidation/Reduction –in a redox reaction, one substance is oxidized and another substance is reduced Oxidized –if electrons are lost Reduced –if electrons are gained Use “OIL RIG” to remember the difference

Redox reactions Example Cl 2(g) + HBr (aq) → HCl (aq) + Br 2(l) Which is oxidized? Which is reduced?

Redox reactions Example NaCl (aq) + Mg (s) → MgCl 2(aq) + Na (s) Which is oxidized? Which is reduced?

Standard Reduction Potential Electricity created by redox reaction: –electrons move from one atom to another atom because of potential differences between these atoms –the current created by these moving electrons is what we call electricity Particles with greater (more positive) reduction potential are more likely to be reduced.

Standard Reduction Potential

Redox Reactions Example: Will this reaction occur as shown below? Cl 2(g) + HBr (aq) → HCl (aq) + Br 2(l)

Redox Reactions Example: Will this reaction occur as shown below? AgCl (aq) + Cu (s) → CuCl (aq) + Ag (s)

Redox Reactions Example: Will this reaction occur as shown below? NaCl (aq) + Mg (s) → MgCl 2(aq) + Na (s)