Lesson Tasks 1 Complete the Chemical Equations worksheet
- Slides: 33
Lesson Tasks 1. Complete the Chemical Equations worksheet using the information in this PPT. 2. Take 1 page of notes, highlighting key point 3. Answer review questions on slide: 4. Chemical Reactions Video with Transcript Annotation a. Files are on the Class Website
Objective: To write balanced chemical equations by inspection. Balanced chemical equation: – Provides qualitative information about the identities and physical states of the reactants and products – Provides quantitative information because it tells the relative amounts of reactants and products consumed or produced in the reaction – The number of atoms, molecules, or formula units of a reactant or product in a balanced chemical equation is the coefficient of that species – Mole ratio of two substances in a chemical reaction is the ratio of their coefficients in the balanced chemical equation Chemical Equations & Reactions
Chemical Reactions You should be able to ★ Classify reactions by type. ★ Write a balanced molecular equation, complete ionic equation, and a net ionic equation. ★ Balance oxidation-reduction reactions. ★ Predict if a precipitate will form using the solubility rules. ★ Predict products of reactions given the chemical names of the reactants.
Organize Your Thoughts Chemical reactions Chemical equations ● ● Balancing equations Predicting products from reactants Chemical equations • Synthesis • Decomposition • Single replacement • Double replacement • Combustion
Describing a Chemical Reaction Indications of a Chemical Reaction – Evolution of heat, light, and/or sound – Production of a gas – Formation of a precipitate – Color change
Signs of Chemical Reactions There are five main signs that indicate a chemical reaction has taken place: release input change in color change in odor production of new gases or vapor input or release of energy difficult to reverse
Chemical Equations aluminum oxide Depict the kind of reactants and products and their relative amounts in a reaction. 4 Al(s) + 3 O 2(g) 2 Al 2 O 3(s) The letters (s), (g), and (l) are the physical states of compounds. The numbers in the front are called stoichiometric coefficients.
Chemical Equations 4 Al(s) + 3 O 2(g) 2 Al 2 O 3(s) aluminum oxide sandpaper 4 g Al + 3 g O 2 yield 2 g Al 2 O 3 This equation means: 4 Al atoms + 3 O 2 molecules yield 2 molecules of Al 2 O 3 or 4 Al moles + 3 O 2 moles yield 2 moles of Al 2 O 3 4 mol Al@27 g/mol 3 mol O 2@32 g/mol 108 g + 96 g 2 mol Al 2 O 3@102 g/mol = 204 g
Chemical Equations Because the same atoms are present in a reaction at the beginning (reactants) and at the end (products), the amount of matter in a system does not change. CHEMICAL EQUATION indicates the reactants and products of a reaction. The Law of Conservation of Matter 100% Chemical Factory 100% 20% 80% REACTANTS → PRODUCTS Kotz web
Chemical Equations Because of the principle of the conservation of matter, An equation must be balanced. It must have the same number of atoms of the same kind on both sides. Lavoisier, 1788 “Father of Modern Chemistry”
Characteristics of Chemical Equations • The equation must represent known facts. • The equation must contain the correct formulas for the reactants and products. • The law of conservation of mass must be satisfied.
Word Equations • A WORD EQUATION describes chemical change using the names of the reactants and products. Write the word equation for the reaction of methane gas with oxygen gas to form carbon dioxide and water. methane + oxygen Reactant CH 4 + 2 O 2 carbon dioxide + water Product CO 2 + 2 H 2 O
Unbalanced and Balanced Equations H Cl Cl H H Cl H 2 + Cl 2 → HCl (unbalanced) reactants H Cl 2 2 H H Cl Cl Cl H 2 + Cl 2 → 2 HCl (balanced) reactants products 1 1 Cl H Cl 2 2 products 2 2
Visualizing a Chemical Reaction 2 Na 10 mole Na ___ + Cl 2 5 mole Cl 2 ___ 2 Na. Cl 10 ? mole Na. Cl ___
Visualizing a Chemical Reaction 2 Na + Cl 2 2 Na. Cl
Meaning of Chemical Formula Chemical Symbol Meaning Composition H 2 O One molecule of water: Two H atoms and one O atom 2 H 2 O Two molecules of water: Four H atoms and two O atoms H 2 One molecule of hydrogen peroxide: Two H atoms and two O atoms
Balancing Chemical Equations Balanced Equation – one in which the number of atoms of each element as a reactant is equal to the number of atoms of that element as a product What is the relationship between conservation of mass and the fact that a balanced equation will always have the same number of atoms of each element on both sides of an equation? Determine whether the following equation is balanced. 2 Na + H 2 O → 2 Na. OH + H 2 2 Na + 2 H 2 O → 2 Na. OH + H 2
Balancing Chemical Equations • Write a word equation for the reaction. • Write the correct formulas for all reactants and products. • Determine the coefficients that make the equation balance.
Balancing Chemical Equations Other examples NO(g) + O 2(g) → NO 2(g) is it balanced? Is this balanced? NO(g) + O(g) → NO 2(g) Is this OK? Is this balanced? NO(g) + ½ O 2(g) → NO 2(g) Is this OK?
Balancing Chemical Equations An important point to remember 2 NO(g) + O 2(g) → 2 NO 2(g) The 2 to the left of NO(g) and NO 2(g) refers to the number of molecules present in the balanced equation. It is a “multiplier” for every atom in the molecule. The subscript 2 in O 2 (g) and NO 2(g) refers to the number of atoms of this type that are present in each molecules (or ionic compound).
Showing Phases in Chemical Equations Solid Phase – the substance is relatively rigid and has a definite volume and shape. Na. Cl(s) H 2 O(l) H 2 O(g) Liquid Phase – the substance has a definite volume, but is able to change shape by flowing. H 2 O(l) Gaseous Phase – the substance has no definite volume or shape, and it shows little response to gravity. Cl 2(g)
Additional Symbols Used in Chemical Equations “Yields”; indicates result of reaction Used to indicate a reversible reaction (s) A reactant or product in the solid state; also used to indicate a precipitate Alternative to (s), but used only to indicate a precipitate (l) A reactant or product in the liquid state (aq) A reactant or product in an aqueous solution (dissolved in water) (g) A reactant or product in the gaseous state
Additional Symbols Used in Chemical Equations Alternative to (g), but used only to indicate a gaseous product Δ 2 atm pressure Reactants are heated Pressure at which reaction is carried out, in this case 2 atm Pressure at which reaction is carried out exceeds normal atmospheric pressure 0 o. C Temperature at which reaction is carried out, in this case 0 o. C Mn. O 2 Formula of catalyst, in this case manganese (IV) oxide, used to alter the rate of the reaction
Formation of a solid: Ag. Cl Ag. NO 3(aq) + KCl(aq) → KNO 3 (aq) + Ag. Cl(s)
lead (II) chloride + potassium iodide K 1+ Pb 2+ Cl 1 Pb. Cl 2 + KI I 1 - potassium chloride + lead (II) iodide Pb 2+ Cl 1 KCl (aq) K 1+ + I 1 - Pb. I 2 (ppt)
Potassium reacts with Water P O W !
Meaning of Coefficients 2 atoms Na 1 molecule Cl 2 2 molecules Na. Cl 2 Na + Cl 2 2 g sodium + 1 g chlorine 2 mol sodium (2 mol Na) x (23 g/mol) 2 Na. Cl = 1 mol chlorine (1 mol Cl 2) x (71 g/mol) 46 g 71 g 117 g 2 g sodium chloride 2 mol sodium chloride (2 mol Na. Cl) x (58. 5 g/mol) 117 g
Classes of Reactions Chemical reactions Precipitation reactions Oxidation-Reduction Reactions Combustion Reactions Acid-Base Reactions
Summary of Classes of Reactions Chemical reactions Precipitation reactions Combustion Reactions Oxidation-Reduction Reactions Synthesis reactions (Reactants are elements. ) Acid-Base Reactions Decomposition reactions (Products are elements. )
A Mixture of Molecules
Review Questions 1. 2. 3. 4. 5. 6. 7. Define catalyst. What information is found in an equation? What symbols are used to represent the states of matter? What is the meaning of “aq”? How do you indicate a catalyst is being used in a reaction? What is activation energy? What the three things does conservation of matter require of chemical equations? 8. What is the procedure for balancing a chemical equation? 9. What is a synthesis reaction? 10. How is a combustion reaction related to a synthesis reaction? 11. What type of reaction is an explosion? 12. Compare decomposition and dissociation. 13. What determines whether one metal will replace another in a single displacement reaction? 14. What is the general form of a double displacement reaction?
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