Chemical Reactions Chapter 10 (page 294)

Essential Question!! Why is learning how to identify & classify chemical reactions and writing equations essential to chemist??

Vocabulary: Section 1 Chemical reaction Chemical equation Reactants Products Law of conservation of mass Unbalanced chemical equation Balanced chemical equation

The alphabet of chemistry More than 200,000 words in the English language Trillions of substances that make up the universe

The language of chemistry Element symbols H, O, Na, Fe Compound formulas H2O, CO2, NaCl Chemical equations 2H2 + O2 2H2O Alphabet of chemistry Words Sentences

Chemical Reactions A chemical reaction is the process of breaking of chemical bonds in one or more substances, and the reforming of new bonds to create new substances. When you make pizza, which changes are physical and which are chemical changes?

Evidence of chemical change Four indicators of chemical change are: Formation of new gas Formation of new solid Release of energy (heat or light) Color change

Products and reactants In chemical reactions, you start with reactants that are combined to make products. The reactants are the starting substances. The products are the new substances which result from the chemical reaction.

Reactants and products In the reaction, methane (a natural gas) is burned or combusted. Some energy is added to get the reaction started.

Chemical Equations In a chemical reaction there is always the material you start with and the material you finish with The starting materials in a reaction are called the reactants The material you end up with is called the product Reactants ----- Products

Assignment Take a new sheet of paper and fold it into three sections Write your name, the title of the chapter and the number On the first section from the sheet of paper, please write six things that you learned from your notes so far that could appear on your test.

Chemical Equations When a chemical reaction is written using chemical formulas and symbols, it is called a chemical equation.

Water is: 2H2 + O2 --- 2H2O

Chemical Equations-is a way to describe a chemical reaction using chemical formulas and symbols Antoine Laurent Lavoisier, established an important principal based on his experiments with chemical reactions. He stated that the total mass of the products of a reaction is equal to the total mass of the reactants. The law of conservation of mass holds true for even a burning mass of wood.

Reactants and products In the reaction, methane (a natural gas) is burned or combusted. Some energy is added to get the reaction started.

Reaction that fuels the space shuttle: Hydrogen burns with oxygen to produce water The “white smoke” is actually water vapor

Chemical equations An arrow is always included between reactants and products. It means “to produce” or “to yield.” to produce Reactants Products “Methane combines with oxygen gas to produce carbon dioxide gas and water vapor.”

Assignment Write a three dollar page summary of what was learned this lesson in your journal using 4 of the vocabulary words Complete page 322 # 1- 6 Honors Chemistry Homework Page 323 # 29 - 37

Vocabulary: Section 2 Balanced chemical equation Products reactants

Cellular respiration What is the number of C, H and O atoms on each side of the reaction arrow?

Balancing Equations The combined mass of the burning wood and oxygen is converted into carbon dioxide and water.

Conservation of mass Lavoisier showed that a closed system must be used when studying chemical reactions. When chemicals are reacted in a closed container, you can show that the mass before and after the reaction is the same.

6 1 8 3 12 2 Not balanced! Cellular respiration Reactants Products Carbon (C) 6 1 Oxygen (O) 8 3 Hydrogen (H) 12 2 Not balanced!

Formula mass The sum of the atomic mass values of the atoms in a chemical formula is called the formula mass.

Molar Mass The mass (in grams) of one mole of a compound is called its molar mass.

Solving Problems What is the molar mass of one mole of CaCO3? Looking for: … molar mass of CaCO3 Given … chemical formula Relationships: no. amu in formula = molar mass in grams

Formula mass CaC03 = 100.19 g 1 mole CaC03 = 100.19 g CaCO3 Solving Problems Solution Formula mass CaC03 = 100.19 g 1 mole CaC03 = 100.19 g CaCO3

Numbers in equations

Balancing equations The law conservation of mass is applied by balancing the number and type of atoms on either side of the equation.

Balancing equations Counting atoms is necessary to balance an equation. How many carbon atoms? How many hydrogen atoms? How many oxygen atoms?

Assignment On the second section of that sheet of paper, please write six things that you learned from your notes so far that could appear on your test.

Strategy to balance a chemical equation: Write down the unbalanced chemical equation. Identify the element that occurs in only one compound on both sides, and balance it first. Continue with the rest of the elements. If a free element is present, it is balanced last. Check each element to make sure that the equation is balanced. Make sure the coefficients are the smallest possible whole numbers.

Steps for balancing If not provided, write the word form of the equation. Calcium carbonate reacts with hydrochloric acid to produce calcium chloride, carbon dioxide and water.

Steps for balancing If not provided, write the chemical equation from the word form.

Steps for balancing Count the number of each type of atom on both sides.

Steps for balancing Add coefficients to balance the equation.

Solving Problems In this reaction, chalcocite (a mineral) reacts with oxygen in the presence of heat. The products are a type of copper oxide and sulfur dioxide. Balance this equation: Cu2S + O2 → Cu2O + SO2

Solving Problems Looking for: Given …the coefficients for each molecule Given … chemical formulas which show types and no. of atoms

Solving Problems Relationships Coefficients can be added in front of any chemical formula in a chemical equation. When a coefficient is added in front of a chemical formula, all atoms in that formula are multiplied by that number. Use common denominators to help choose coefficients to try.

Solving Problems Solution- Trial and error

Assignment Write a three dollar summary of what was learned this lesson in your journal using 4 of the vocabulary words Complete page 322 # 7-14 Honors Chemistry Homework Page 324 # 53 - 63

Vocabulary: Section 3 Decomposition reaction Enthalpy Single displacement Double displacement Precipitate Solubility Polymerization reactions Polymer Exothermic reaction Endothermic reaction Enthalpy Thermochemical equation Enthalpy of formation Photosynthesis Energy barrier Spontaneous reaction Chemical engineering Green chemistry

Chemical equations tell stories… Reactants Products … and stories can be put into different categories Nonfiction Science fiction Adventure Romance History Psychology Children’s literature …

Addition reactions The process of creating large molecules from small ones is called polymerization.

Addition reactions In an addition reaction, two or more substances combine to form a new compound.

Decomposition reactions A chemical reaction in which a single compound is broken down to produce two or more smaller compounds is called a decomposition reaction.

Single Displacement In a single-displacement reaction, one element replaces a similar element in a compound.

Double Displacement In a double-displacement reaction, ions from two compounds in solution exchange places to produce two new compounds. One of the compounds formed is usually a precipitate that settles out of the solution, a gas that bubbles out of the solution, or a molecular compound such as water.

Precipitation reactions A precipitate is a new solid product that comes out of solution in a chemical reaction. The formation of a cloudy precipitate is evidence that a double-displacement reaction has occurred.

Precipitation The limewater test for carbon dioxide is a precipitation reaction.

Precipitate reaction Solubility rules for common ionic compounds in water

Combustion reactions A combustion reaction, also called burning, occurs when a substance such as wood, natural gas, or propane combines with oxygen and releases a large amount of energy in the form of light and heat.

Combustion reactions What do reactants like wood, natural gas, and propane have in common?

Assignment On the third section of that sheet of paper, please write six things that you learned from your notes so far that could appear on your test.

Oxidation and Reduction Oxidation is the loss of electrons Reduction is the gain of electrons Stronger nonmetals are reduced and weaker nonmetals become oxidized Generally: Metals become oxidized Nonmetals become reduced

Objectives Students will be able to: Contrast endergonic and exergonic reactions. Contrast endothermic and exothermic reactions. Explain why activation energy is needed to begin chemical reactions. Describe what happens when ionic compounds are dissolved in water.

Energy and Reactions Energy is involved in chemical reactions in two ways: to break some (or all) bonds between atoms in the reactants so the atoms can form new bonds or when the atoms or products form new bonds to make new products.

Two Types of Reactions We classify chemical reactions based on how the energy of the reactants compares to the energy of the products.

Exothermic reactions If forming new bonds releases more energy than it takes to break the old bonds, the reaction is exothermic.

Exothermic reactions A good example is the reaction of hydrogen with oxygen. Once started, exothermic reactions tend to keep going as each reaction releases more energy to fuel neighboring molecules.

Endothermic reactions If forming new bonds in the products releases less energy than it took to break the original bonds, the reaction is endothermic.

Endothermic reactions An important endothermic reaction is photosynthesis. Plants need energy from sunlight to make glucose and oxygen from carbon dioxide and water.

Activation Energy Activation energy is the energy needed to begin a reaction and break chemical bonds in the reactants.

Activation Energy This is why a flammable material like gasoline does not burn without a spark or flame.

Carbon Reactions Carbon dioxide and other atmospheric gases are called “greenhouse gases.” Scientists believe the rise in amount of greenhouse gases will result in rises in sea level and changes in weather.

Assignment On the first section of the back side of that sheet of paper, please write six things that you learned from your notes so far that could appear on your test.

Examples of Endothermic Reactions Most of the reactions used in industry to produce useful materials require more energy than they produce. One process that uses endothermic reactions is the refining of ores to produce useful metals.

Examples of Endothermic Reactions Most of the reactions used in industry to produce useful materials require more energy than they produce. The reaction taking place inside an instant cold pack is endothermic.

Catalyst and Inhibitors A catalyst is a substance that speeds up a chemical reaction without being permanently changed in the process Inhibitors are substances that are used to slow down a chemical reaction

Examples of Endothermic Reactions When you squeeze the plastic bag the water reacts with the ammonium nitrate crystals, and the reaction dissolves the ionic bonds in the ammonium nitrate.

Examples of Endothermic Reactions The reaction is also a dissolution reaction. Dissolution occurs when an ionic compound (like ammonium nitrate) dissolves in water to make an ionic solution.

Assignment Write a three dollar summary of what was learned this lesson in your journal using 4 of the vocabulary words Complete page 322 # 15-23 Honors Chemistry Homework Page 325 # 39 - 41

Test: - Next week Tuesday or Thursday depending on your block Homework requirement: Learn all terms and concepts learned on this topic Make sure you have all assignments between page 322 - 325 completed and turned in by your test date.