Chapter 7: Chemical Reactions and Quantities
Combination Reactions
-In a combination reaction: -two or more elements form one product. -simple compounds combine to form one product
-7.6 Mole Relationships in Chemical Equations
-In the chemical reaction of Fe and S, the mass of the reactants is the same as the mass of the product, Fe2S3: 2Fe(s) + 3S(s)-->Fe2S3(s)
Mole of Atoms
-1 mole of an element = 6.02 × 10^23 atoms of that element -1 mole of carbon = 6.02 × 10^23 atoms of carbon 1 mole of sodium = 6.02 × 10^23 atoms of sodium
7.1 Equations for Chemical Reactions
-A chemical change occurs when a substance is converted into one or more new substances that have different formulas and different properties
7.4 The Mole (Not on Lab midterm)
-A counting term states a specific number of items. The terms dozen, case, gross, and ream are used to count the number of items present. -
Limiting Reactant
-A limiting reactant in a chemical reaction: -is the substance that is used up first. -limits the amount of product that can form. -The reactant that does not completely react and is left over at the end of the reaction is called the excess reactant.
7.7 Mass Calculations for Reactions (not on Lab midterm)
-A mixture of acetylene and oxygen undergoes combustion during the welding of metals. We can calculate the mass of acetylene used to weld a specific mass of metal.
Mole-Mole Factors from an Equation
-A mole-mole factor is a ratio of the moles for any two substances in an equation. -2Fe(s) + 3S(s)-->Fe2S3(s) -factors would be:
7.9 Energy in Chemical Reactions (not on Lab midterm)
-Almost every chemical reaction involves the loss or gain of energy. When cold packs are activated, an endothermic reaction takes place.
Conversion Factor, Avogadro's Number
-Avogadro's number, 6.02 × 1023, can be written as an equality and as two conversion factors. Equality: -1 mole = 6.02 × 10^23 particles -Conversion Factors: 1 mole/ 6.02 × 10^23 particles or 6.02 × 10^23 particles/1 mole
Equations, Mass of A−Mass of B
-Given a balanced equation, convert the mass of substance A to substance B by: -first, converting the mass of substance A to moles using the molar mass of A; -second, converting moles of substance A to moles of substance B using the mole-mole ratio of B to A in the balanced equation; and -third, converting moles of substance B to grams using the molar mass of B.
Chemistry Link to Health: Toxicity of CO
-Hemoglobin is the protein in the blood that transports O2 to cells. When hemoglobin bound to CO (COHb) reaches -10%, a person may experience shortness of breath, mild headache, and drowsiness. -30%, a person may experience more severe symptoms, including dizziness, mental confusion, severe headache, and nausea. -50%, a person could become unconscious and die if not treated immediately with oxygen.
Study Check
-Identify each of the following as oxidation or reduction: A. Sn(s)-->Sn4+(aq) + 4e− Oxidation B. Fe3+(aq) + 1e− -->Fe2+(aq) Reduction C. Cl2(g) + 2e− -->2Cl− (aq) Reduction
Identifying a Balanced Equation
-In a balanced chemical equation: -no atoms are lost or gained. -the number of atoms on the reactant side is equal to the number of atoms on the product side for each element -number of atoms aka number of moles (the coefficients in a balanced equation)
7.2 Types of Reactions
-In a combustion reaction, a candle burns using the oxygen in the air -Chemical reactions can be classified as: -combination reactions. -decomposition reactions. -single replacement reactions. -double replacement reactions. -combustion reactions. -Some reactions may fit into more than one reaction type -Redox can be: single replacement, combination, decomposition -Single replacement: always redox
Combustion Reactions
-In a combustion reaction: -a carbon-containing compound burns in oxygen gas to form carbon dioxide (CO2) and water (H2O). -energy is released as a product in the form of heat. -CH4(g) + 2O2(g) -->CO2(g) + 2H2O(g) + energy -C3H8(g) + 5O2(g) -->3CO2(g) + 4H2O(g) + energy
Decomposition Reactions
-In a decomposition reaction, one substance splits into two or more simpler substances.
Double Replacement Reactions
-In a double replacement reaction, the positive ions in the reactant compounds switch places.
Single Replacement Reactions
-In a single replacement reaction, one element takes the place of a different element in another reacting compound.
Exothermic Reactions Released
-In an endothermic reaction, -heat is absorbed. -the energy of the products is greater than the energy of the reactants. -heat is a reactant (added). -N2(g) + O2(g) + 180 kJ--> 2NO(g) -ΔH = +180 kJ
Exothermic Reactions Released
-In an exothermic reaction, -heat is released. -the energy of the products is less than the energy of the reactants. -heat is a product. -H2(g) + Cl2(g)-->2HCl(g) + 185 kJ -ΔH = −185 kJ
Oxidation−Reduction
-In an oxidation-reduction reaction, electrons are transferred from one substance to another. -The green patina on the Statue of Liberty is due to the oxidation of copper metal as it forms a green solid, CuO. 2Cu(s)--> 2Cu2+(s) + 4e− oxidation O2(g) + 4e− -->2O2− (s) reduction Makes: 2Cu(s) + O2(g)--> 2CuO(s)
Oxidation-Reduction of CH3OH
-In many biochemical oxidation-reduction reactions, the transfer of hydrogen atoms is necessary for the production of energy. -For example, the body metabolizes methyl alcohol, a poisonous substance, by the following reactions: CH3OH-->H2CO +2H Oxidation: loss of H atoms methyl alcohol formaldehyde 2H2CO + O2--> 2H2CO2 Oxidation: addition of O atoms formaldehyde formic acid 2H2CO2 + O2-->2CO2 + 2 H2O Oxidation: addition of O atoms formic acid -The intermediate products are toxic, causing headaches and possible death because they interfere with key reactions in cells.
Calculating Moles of Product from a Limiting Reactant
-In many reactions, there is a limiting reactant that determines the amount of product that can be formed. -Given a chemical reaction, from each reactant we can: -calculate the amount of product possible when it is completely consumed. -determine the limiting reactant, the one that runs out first and produces the smaller amount of product.
Chemistry Link to Health: Cold Packs and Hot Packs
-Inside the cold pack, solid ammonium nitrate (NH4NO3) is separated from the compartment containing water. When the cold pack is hit or squeezed, the compartments break and the NH4NO3 mixes with the water in an endothermic reaction. -Inside the hot pack, solid calcium chloride (CaCl2) is separated from the compartment containing water. -When the cold pack is hit or squeezed, the compartments break and the CaCl2 mixes with the water in an exothermic reaction.
Calculations Using Molar Mass
-Molar mass conversion factors: -are fractions (ratios) written from the molar mass. -relate grams and moles of an element or compound. -for methane, CH4, used in gas stoves and gas heaters, is 1 mole of CH4 = 16.05 g of CH4 (molar mass equality) Conversion factors:
7.3 Oxidation−Reduction Reactions (not on Lab midterm)
-Rust forms when the oxygen in the air reacts with iron. In this process, electrons are transferred from one substance to another. -An oxidation-reduction reaction provides us with energy from food. provides electrical energy in batteries. occurs when iron rusts: 4Fe(s) + 3O2(g)-->2Fe2O3(s)
Avogadro's Number
-Small particles such as atoms, molecules, and ions are counted using the mole, a unit called Avogadro's number that contains 6.02 × 1023 items. -1 mole = 6.02 × 1023 items -Avogadro's number: 602 000 000 000 000 000 000 000 = 6.02 × 1023 -Avogadro's number is named for Amedeo Avogadro (1776-1856), an Italian physicist.
Energy Units for Chemical Reactions
-The SI unit for energy is the joule (J). -Often the unit of kilojoules (kJ) is used to illustrate the amount of energy lost or gained in a chemical reaction - 1 kilojoule (kJ) = 1000 joules (J)
Law of Conservation of Mass
-The law of conservation of mass indicates that in an ordinary chemical reaction: -matter cannot be created or destroyed. -no change in total mass occurs. -the mass of products is equal to the mass of reactants. -Consider the following equation: 2Fe(s)+3S(s)-->Fe2S3(s) We can read this as 2 moles of Fe + 3 moles of S--> 1 mole of Fe2S3
7.5 Molar Mass and Calculations
-The molar mass of an element is useful to convert moles of an element to grams, or grams to moles. -For example, 1 mole of sodium has a mass of 22.99 grams. -The molar mass is the mass of 1 mole of an element. the atomic mass expressed in grams. Ex: 1 mole C = 12.01 g 1 mole Li = 6.941 g
Characteristics, Oxidation−Reduction
-The particular definition of oxidation and reduction depends on the process that occurs in the reaction -Oxidation: -always involves a loss of electrons. -may also be seen as an addition of oxygen. -may also be seen as the loss of hydrogen atoms. -Reduction: -always involves a gain of electrons. -may also be seen as the loss of oxygen. -may also be seen as the gain of hydrogen.
Chemical Changes
A chemical change: -occurs when a substance is converted into one or more substances with different formulas and different properties. -may be observed by the formation of bubbles, a change in color, production of a solid, or heat that is produced or absorbed.
Guide to Calculations Using Heat of Reaction: example
solved:
Limiting Reactant, Mass of Product example
solved:
Limiting Reactant, Moles of Product example
solved:
Mass N2 − Mass NH3 example:
solved:
Chemistry Link to Health: Toxicity of CO
-Carbon monoxide (CO): -is a colorless, odorless, poisonous gas. -attaches to hemoglobin molecules when inhaled. -reduces the amount of oxygen gas (O2) that can reach the cells. -causes a person to experience a reduction in exercise capability, visual perception, and manual dexterity.
Oxidation-Reduction in Biological Systems, Coenzyme FAD
-The biochemical molecule FAD (flavin adenine dinucleotide) can be reduced to FADH2 by the transfer of two hydrogen atoms (2H+ and 2e−). -image on charts handout
Heat of Reaction
-The heat of reaction is the amount of heat absorbed or released during a reaction that takes place at constant pressure. The change in energy occurs when: -reactants interact. -bonds break apart. -products are formed. -The heat of reaction or enthalpy change, symbol ΔH, is the difference between the enthalpy of the products and enthalpy of the reactants. ΔH = Hproducts − Hreactants
Limiting Reactant, Mass of Product
-The quantities of reactants can also be given in grams. The calculations to identify the limiting reactant are: -first, convert the grams of each reactant to moles of reactant using molar mass conversion factors; -second, use mole-mole factors to convert moles of reactant to moles of product; and -third, use molar mass to convert the moles of product to grams of product. The reactant that produces the least amount of product is the limiting reactant.
Moles of Elements in a Formula
-The subscripts in a formula show: -the relationship of atoms in the formula. -the moles of each element in 1 mole of compound. Ex: Aspirin: C9H8O4 1 molecule: 9 atoms of C, 8 atoms of H,4 atoms of O 1 mole:9 moles of C,8 moles of H, 4 moles of O -Subscripts are used to write conversion factors for moles of each element in 1 mole of a compound. Ex: For 1 mole of aspirin, C9H8O4, the possible conversion factors are:
Calculating Heat Changes
-The value of ΔH refers to the heat change for each substance in the balanced equation. -For the decomposition reaction, 2H2O(l)-->2H2(g) + O2(g) ΔH = +572 kJ 2H2O(l) + 572 kJ 2H2(g) + O2(g) -We can write the following conversion factors:
Writing a Chemical Equation and Symbols used
-To write a chemical equation: -an arrow separates reactants from the products (). -reactants are written on the left side of the arrow; products are written on the right side of the arrow. -multiple reactants or products are separated by a + sign. -the delta (Δ) sign indicates heat is used to start the reaction. -reactant + reactant--->product + product -physical states of compounds are denoted in parentheses following the compound: solid (s), liquid (l), gas (g), and aqueous (aq) or dissolved in water.
Chemistry Link to Health: Toxicity of CO
-When a propane heater, fireplace, or woodstove is used to burn fuel, adequate ventilation is needed. -When the oxygen supply is limited, incomplete combustion occurs -from burning gas, oil, or wood and produces CO, carbon monoxide. -according to the following reaction: 2CH4(g) + 3O2(g)-->2CO(g) + 4H2O(g) + heat
Actual, Theoretical, and Percent Yield
-When the reaction does not go to completion, or some of the reactant or product is lost, the amount of product produced may be less. -Theoretical yield is the maximum amount of product, which is calculated using the balanced equation. -Actual yield is the amount of product actually obtained. -Percent yield is the ratio of actual yield to theoretical yield. -formula:
7.8 Limiting Reactants, Percent Yield (not on Lab midterm)
-When you make a peanut butter sandwich, you need 2 slices of bread and 1 tablespoon of peanut butter. The reactant that runs out first is called the limiting reactant.