Unit A: Chemistry

1. Chemical change is a process that involves recombining atoms and energy flows. Unit A: Chemistry

2. In this unit, you will learn about... • General Outcome #3 – Identify and classify chemical changes, and write word and balanced chemical equations for significant chemical reactions, as applications of Lavoisier’s law for conservation of mass • ROCK – describe the evidence for chemical changes (energy change, formation of gas or precipitate, color or odour change, change in temperature) • ROCK – differentiate between endothermic and exothermic chemical reactions

3. ROCK – translate word equations to balanced chemical equations and vice versa for chemical reactions that occur in living and non living systems • ROCK – classify and identify categories of chemical reactions (formation, decomposition, hydrocarbon combustion, single replacement, double replacement) • ROCK – predict the products of formation (synthesis) and decomposition, single and double replacement and hydrocarbon combustion chemical reactions, when given the reactants • ROCK – interpret balanced chemical equations in terms of moles of chemical species and relate the mole concept to the law of conservation of mass • SAND – identify chemical reactions that are significant in societies • SAND – define the mole as the amount of an element containing 6.02 X 1023 atoms (Avogadro’s number) and apply the concept to calculate quantifies of substances of other chemical species • SAND – provide examples of household, commercial and industrial processes that use chemical reactions to produce useful substances and energy

4. The Ultimate Chemical Reaction • What do you think would be one of the coolest things to experience??

5. A3.1: Important Examples of Chemical Change Unit A: chemistry

6. In this section, you will learn about... • General Outcome #3 – Identify and classify chemical changes, and write word and balanced chemical equations for significant chemical reactions, as applications of Lavoisier’s law for conservation of mass • ROCK – describe the evidence for chemical changes (energy change, formation of gas or precipitate, color or odour change, change in temperature) • ROCK – differentiate between endothermic and exothermic chemical reactions • SAND – identify chemical reactions that are significant in societies • SAND – provide examples of household, commercial and industrial processes that use chemical reactions to produce useful substances and energy

7. Did you know?? • Slicing an onion causes your eyes to sting because of a chemical reaction. Slicing ruptures the onion’s cells allowing substances to mix. A gas is produced and reacts with the water in your eyes – producing dilute sulfuric acid!

8. Important Examples of Chemical Change • When was the last time you watched an awesome display of fireworks? Fireworks is one example of chemical change (occurs when a substance or substances react in a chemical reaction to create a different substance or substances) occurring. Other examples of chemical change include dough rising, the changing taste of food cooking on a barbecue, the combustion of fuel in a motor vehicle, a glowing glow stick, and the changing temperature of a hot or cold pack.

9. Important Examples of Chemical Change • The substances that react are called reactants and the new substances that are produced are called products • The products have completely different properties than the reactants

10. Energy Flow through Systems • On p. 79, answer Minds On... questions 1-4

11. Energy Flow through Systems • Which of these processes involve a release of energy? • Fireworks (a) and the glow stick (d) involve a release of energy. Fireworks release heat, light, and sound energy. The glow stick releases light energy. • Which involve the absorption of energy? • The boiling water (b) and the baking (c) involve the absorption of energy. Both absorb heat energy produced by a gas flame or an electric current passing through an element.

12. Energy Flow through Systems • Which are chemical changes? • Chemical change involves a change to the composition of the substance. Therefore, chemical changes occur in (a), (c), and (d). • Which are physical changes? • Physical change involves a change of state (e.g., liquid to gas). A physical change occurs in (b).

13. Reactions That Form Gases • Recall: evidence of chemical reactions include the formation of gases and precipitates. • Familiar examples of chemical reactions that result in the formation of gases are breads and cakes rising and the inflation of an automobile air bag.

14. Reactions That Form Solids • Some reactions form a solid that hardens over a short period of time. Epoxy glue is one example.

15. Showing States in Chemical Formulas • Recall: (s), (l), (g), (aq) are the subscripts that refer to the substances state at room temperature. It is important to always give as much information as possible about a reaction. • The following are guidelines for the states of substances at room temperature

16. Showing States in Chemical Formulas • Elements • Metals are solid, except mercury, which is a liquid • Most of the diatomic elements are gases H2(g), N2(g), O2(g), F2(g) and Cl2(g). Bromine is a liquid and iodine is a solid: Br2(l) and I2(s) • Sulfur, phosphorus and carbon are solids

17. Showing States in Chemical Formulas • Compounds • All ionic compounds are solid at room temperature • An ionic compound that is very soluble is shown as aqueous when it is dissolved in water. An ionic compound that is slightly soluble is usually shown as solid, even when it’s in water. • Molecular compounds are very difficult to predict. The smaller the molecules are, the more they tend to be gases. The larger they are, the more they tend to be liquids and solids. For example, CH4(g) is a gas (natural gas), C6H14(l) is a liquid component of gasoline and C18H38(s) is bees wax.

18. Energy Changes • Energy flow is an essential part of any chemical reaction, sometimes energy is absorbed and other times energy is released.

19. Exothermic Reactions • THE AUTOMOTIVE BATTERYA lead-acid storage battery is an electrochemical device that produces voltage and delivers electrical current. The battery is the primary "source" of electrical energy used in vehicles today. It's important to remember that a battery does not store electricity, but rather it stores a series of chemicals, and through a chemical process electricity is produced. Basically, two different types of lead in an acid mixture react to produce an electrical pressure called voltage. This electrochemical reaction changes chemical energy to electrical energy and is the basis for all automotive batteries. • Exothermic reactions – chemical reaction that release energy usually in the form of heat, light or electricity

20. Exothermic Reactions • Another important exothermic reaction is the combustion of fossil fuels: coal, oil and natural gas • Combustion – chemical reaction that occurs when oxygen reacts rapidly with a substance to form a new substance and gives off energy (also called “burning”)

21. Exothermic Reactions • For example, coal is used to produce electricity, the heat released by coal combustion is used to make steam, which drives turbines that produce electricity. • This process produces carbon dioxide, which is a greenhouse gas that contributes to climate change coal + oxygen carbon dioxide + energy

22. Endothermic Reactions • Endothermic reaction – chemical reaction that absorbs energy • For example, in a cold pack, it contains chemicals that absorb energy directly from the environment. When you squeeze the package, you break a container inside the pack that keeps the chemicals separate from each other. When they mix and react, they absorb energy and the whole mixture cools down

23. Biochemical Reactions • Two examples of chemical reactions important to life on Earth are photosynthesis and respiration. These two biochemical reactions (may be endothermic or exothermic) form the basis of life as almost all food produced on Earth begins with photosynthesis.

24. Characteristics of Chemical Reactions • Recall: All chemical reactions have these characteristics • All reactions involve the production of new substances with their own characteristics (state at room temperature, melting point, colour and density) • All reactions involve the flow of energy. This may be detected by a change in temperature during the reaction. Endothermic reactions absorb energy and exothermic reactions release energy.

25. Characteristics of Chemical Reactions • When new substances form in chemical reactions, sometimes changes of state can be observed. For example, the formation of a gas (bubbles) or a solid (precipitate) • All chemical reactions are consistent with the law of conservation of mass Any ideas as to what this means?

26. Conservation of Mass • In 1789, a French chemist, Antoine Lavoisier, came to a very important conclusion. Before we discuss this, try to explain this; • Suppose 23.0g of magnesium metal is burned in pure oxygen. When all of the white powder is carefully collected and placed on a scale, its mass is 39.0g. How can it weigh 16g more?? How does this make sense??

27. Conservation of Mass • First, let’s look at Lavoisier’s work. He stated that: when a system of chemicals reacts completely, the total mass of all of the reactants equals the total mass of the products. In other words, in chemical processes, the most important property to be conserved is the number of atoms of each kind that are present. Unlike nuclear processes, chemical reactions do not create or destroy atoms, or change one kind of atom into another. They only reshuffle the atoms that were originally present into different molecular combinations. What we would like to be able to do is to count each kind of atom before and after a reaction and make sure that none has been gained or lost.

28. Still...how can you start with 23g and end up with 39g??

29. Conservation of Mass • Is Lavoisier’s conclusion wrong?? • No, it’s not wrong, it’s actually telling us that 16g of oxygen reacted with the 23g of magnesium metal. The difference in mass means that there is a reactant that we can’t see – some new form of matter. The difference of mass between the magnesium and white powder product also gives us the mass of this unseen compound. • His conclusion is called the law of conservation of mass

30. A3.2: Writing Chemical Equations Unit A: chemistry

31. In this section you will learn about... • General Outcome #3 – Identify and classify chemical changes, and write word and balanced chemical equations for significant chemical reactions, as applications of Lavoisier’s law for conservation of mass • ROCK – translate word equations to balanced chemical equations and vice versa for chemical reactions that occur in living and non living systems

33. Writing Chemical Equations • Chemical change involves chemical reactions. To record what occurs in a chemical reaction, chemists use a balanced chemical equation made up of chemical formulas.

34. Symbolizing Chemical Change • To write a chemical equation, you need to know what substances react (the reactants) and what new substances form (the products). This requires you to; • careful observations • knowledge of what substances are present at the start of the reaction • the ability to analyze the materials produced by the reaction

35. Symbolizing Chemical Change • Recall: chemical change is often accompanied by visible events such as; • change in color • production of gas (bubbles) • release of heat (increased temperature) • appearance of a substance that is only slightly soluble (cloudiness)

36. Writing Word Equations • Consider the chemical reaction between a piece of magnesium metal with hydrochloric acid. We can describe the reaction with the following sentence; • solid magnesium metal reacts with aqueous hydrochloric acid to produce aqueous magnesium chloride and hydrogen gas. • Which are the products? Which are the reactants?

37. Writing Word Equations • The word equation for this reaction is; magnesium + hydrochloric acid magnesium chloride + hydrogen gas • The “+” sign groups the reactants and the arrow separates the reactants from the products (which is read “produces”), then the products are separated by a “+” sign as well

38. Writing Word Equations • Another example; • An iron nail is placed in a solution of copper (II) chloride iron + copper (II) chloride iron (II) chloride + copper Don’t worry about not knowing the products of a chemical reaction, we’ll go through those more in depth later!

39. Writing Balanced Formula Equations • Formula equation – a chemical equation that uses the reactants and products in a chemical reaction • Because mass is conserved in a chemical reaction, you need to write a balanced formula equation (a formula equation that has the same number of atoms of each element in both the reactants and products)

40. Writing Balanced Formula Equations • Let’s look at the formula for water; hydrogen + oxygen water H2 (g) + O2 (g) H2O(l) This is called a skeleton equation because it identifies the substances involved in the reaction but it is not balanced.

41. Writing Balanced Formula Equations • How do you know the correct proportions? • Recall: the law of conservation of mass – the mass of the reactants must equal the mass of the products H2 (g) + O2 (g) H2O(l) • Follow these steps: • Count the number of oxygen and balance H2 (g) + O2 (g) → 2 H2O(l) • Count the number of hydrogen and balance 2 H2 (g) + O2 (g) → 2 H2O(l) →

42. Writing Balanced Formula Equations • Try the following N2 (g) + H2(g) → NH3(g) • Count the number of nitrogen and balance N2 (g) + H2(g) → 2NH3(g) • Count the number of hydrogen and balance N2 (g) + 3H2(g) → 2NH3(g)

43. Writing Balanced Formula Equations • There is no specific element to try to balance first, if you’re having trouble with one element and it won’t seem to balance then start with one of the other elements first!

44. Writing Balanced Formula Equations • Try to balance the following: • O2 (g) + CH4(g) → CO2(g) + H2O(g) • 2O2 (g) + CH4(g) → CO2(g) + 2H2O(g) • Fe(NO3)2(aq) + Na3PO4(aq) → NaNO3(aq) + Fe3(PO4)2(s) • 3Fe(NO3)2(aq) + 2Na3PO4(aq) → 6NaNO3(aq) + Fe3(PO4)2(s)

45. A3.3: Five Common Types of Chemical Reactions Unit A: Chemistry

47. In this section, you will learn about... • General Outcome #3 – Identify and classify chemical changes, and write word and balanced chemical equations for significant chemical reactions, as applications of Lavoisier’s law for conservation of mass • ROCK – classify and identify categories of chemical reactions (formation, decomposition, hydrocarbon combustion, single replacement, double replacement) • ROCK – predict the products of formation (synthesis) and decomposition, single and double replacement and hydrocarbon combustion chemical reactions, when given the reactants

48. Five Common Types of Chemical Reactions • Chemists have looked at many different types of reactions and found some common characteristics. From the vast array of reactions, a few types have emerged and have also allowed us to predict the outcome of many chemical reactions by examining the reactants. • The five common types of chemical reactions are formation, decomposition, hydrocarbon combustion, single replacement and double replacement

49. Formation Reactions • Formation reaction – two elements combine to form a compound (also known as composition or synthesis) • element + element = compound OR • A + B = AB

50. Formation Reactions • Example: • Word Equation: • sulfur + oxygen sulfur dioxide • Skeleton Equation: • S8(s) + O2(g) SO2(g) • Balanced Equation: • 1S8(s) + 8O2(g)8SO2(g)