Unit 3: Chemical reactions, energy changes, redox reactions

Synthesis Reaction

when elements or simple compounds are combined to form a more complex compound

Ex: 2Mg + O₂ → 2MgO

Decomposition Reaction

when a single compound is separated into 2 or more compounds and/or elements

Ex: HgO + Heat → Hg + ½ O

Acid-based reaction

a reaction where an acid reacts with a base to form a water and a salt

Ex: HCl (aq) + NaOH (aq) → NaCl (aq) + H₂O (l)

Acid

any substance that donates a proton in water; increases the concentration of H⁺ ions

• Look for substances that start with a H or have a -COOH group

  • HCl, H₂SO₄, CH₃COOH

Base

any substance that accepts a proton in water; produces OH^-

• look for substances that contain OH

  • KOH, Ca(OH)₂

aqueous (aq)

dissolved in water

Redox Reactions

a chemical reaction where electrons are transferred between substances

Ex: Zn + Cu²⁺ → Zn²⁺ + Cu

Oxidation

a loss of electrons

Reduction

a gain of electrons

Oxidizing Agent

causes something to be oxidized by accepting e^- ; the oxidizing agent itself is reduced

Reduction agent

causes something to be reduced by donating e^- ; the reduction agent itself is oxidized

Hydrocarbon combustion

when a covalent substance containing H, C, sometimes O is ignited and reacts with oxygen in the air to combust

Ex: C₄H₁₀ + 13/2 O₂ → 4CO₂ + 5H₂O

products of Hydrocarbon Combustion always include ___ and ___

CO₂ and H₂O

if the reactants of Hydrocarbon Combustion reactions contain non H or C elements they will ….

combine with O to form various gasses

Ex: SC₂H₅ + 17/2 O₂ → 4 CO₂ + 5 H₂O + 2 SO₂

Precipitation

when ions dissolved in water rearrange themselves to form a sold as one of the rearranged ions was insoluble

Precipitate

the solid formed in a precipitation reaction

Spectator Ions

ions that started as free ions and ended as free ions

Compounds that are always soluble

• Compounds with nitrates (NO^-₃)

• Compounds with any Group 1 metal salts (Na, K, Li)

• Compounds with ammonium (NH⁺₄)

• Compounds with Acetates (CH₃COO^-)

Compounds that are usually insoluble

• Compounds with carbonates (CO^2-₃)

• Compounds with phosphates (PO₄^3-)

• Compounds with hydroxides (OH^-)

Hydroxide

OH^-

Nitrate

NO^-₃

Acetate

C₂H₃O₂^-

Cyanide

CN^-

Permanganate

MnO^-₄

Carbonate

CO^2-₃

Sulfate

SO^2-₄

Dichromate

Cr₂O₇^2-

Phosphate

PO^3-₄

Ammonium

NH⁺₄

Limiting reagent

the reactant that gets used up first and limits how much product can form

Excess Reagent

the reactant that is left over

the molar volume of any gas at STP

22.4 L/mol

when a hydrocarbon is combusted all of the carbon will end up in ___ and all of the hydrogen will end up in ___

CO₂; H₂O

Gravemetric analysis

the use of precipitation reactions to determine the identity of the unknown substance

Enthalapy

the measure of the energy that is released or absorbed by the substance when bonds are broken or formed during a reaction

Rules of enthalapy

• when bonds are broken; energy is released

• when bonds are formed; energy is absorbed

change in enthalpy equation

\Delta H = H_Products - H_Reactants

Exothermic reactions

when more energy is released when the products form a bond than when the reactants break a bond

• negative\Delta H

Endothermic Reactions

when more energy is required to break a bond in reactants than is released when bonds form in products

• Positive \Delta H

activated complex

highest point on an energy diagram and where all bonds are broken at this point

E_a

Energy required to reach activated complex

E’_a

energy required for reverse reactions to form product bonds

Catalyst

lowers the E_a and the E’_a

Oxidation states

track which reactants are gaining or losing e^-

6 rules of oxidation states

• neutral atoms not bonded to atoms of other elements have oxidation state of 0

• any ion has an oxidation state equal to the charge on that ion

• In most compounds the oxidation state on Oxygen is -2

  • Exception: In Hydrogen peroxide H₂O₂; Oxygen is -1

• When bonded to a metal Hydrogen has an oxidation state of -1 and when bonded to a nonmetal hydrogen has an oxidation state of +1

• In the absence of Oxygen the element with the highest electronegativity will take an oxidation state equal to its most common charge

• The combined oxidation states in a neutral compound must add up to 0 and in a polyatomic ion it must add up to the charge on that ion

Titration

slow addition of a known solution into an solution of an unknown concentration to determine the concentration

electric potential

the potential for a half reaction to occur the higher the potential the more likely it is

Anode

where oxidation occurs

Cathode

where reduction occurs

Galvanic cell

a cell that houses a spontaneous redox reaction to produce electricity

the purpose of salt bridges in galvanic cells is to….

keep both cells neutral or else the voltage drops to 0

Electrolytic Cell

houses a non-spontaneous redox reaction and required energy

Electroplating

a electrolytic proccess where a metal ion is reduced and deposited as solid metal

moles of e^- equation

\frac{coulumbs}{96500}