CHEM 1021 Lecture Notes - Lecture 5: Iron(Iii) Oxide, Aluminium Oxide, Reagent

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Rooted in dalton"s atomic theory - matter is neither created nor destroyed, only rearranged. The type of atom present at the start is the same at the end (ie. h2o (aq) -> h2o2 (aq)) Chemical reactions are conversions of substances (and thus, chemical changes) The starting substance is the reactant; the newly created substance is the product (ie. formation of. H2o; elemental h2 and o2 reactant yield compound h2o product) Keep in mind that the h2 in the product is not elemental h2. Indications of a chemical reaction include changes in color, changes in odor, the production of gas (aka vapor), the input or release of energy, and the difficulty of reversing such a reaction. Chemical equations are a symbolic means of representing chemical reactions (ie. reactant 1 + Reactant 2 -> product 1 + product 2) Arrow means yields , plus sign means and (number of reactants and products vary)

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Chemical Reactions and Equations Learning objectives To observe physical and chemical properties associated with chemical changes To be able to give evidence for the occurrence of a chemical reaction To write a balanced chemical equation To identify areaction as a combination, decomposition, precipitation, single or double replacement, or combustion reaction ntroduction When a substance undergoes a physical change, it changes its appearance but not its composition. For example, when ice melts to form water, it undergoes a physical change from solid to liquid. In a chemical change, the composition of a substance is changed to give a new substance with different physical and chemical properties. For example, when silver tarnishes, the shiny silver (Ag) changes to a dull gray silver sulfide (AgaS). Not only has the chemical formula changed from Ag to Agus, but also the physical properties (shininess) of the substance have changed. Some examples of physical and chemical changes are listed in Table 1 below. Table 1. Comparison of Physical and Chemical Changes Examples of Physical changes Examples and Evidence of Chemical Changes Change in state (melting, freezing, evaporating Formation of a gas (bubbles) subliming) Formation of a solid (precipitate) Change in size Tearing Change in Color Heat is given off or absorbed A solid dissolving in a solvent In a chemical reaction, atoms in the reactants are rearranged to produce new combinations of atoms in the products. However, the total number of atoms of each element in the reactants is equal to the total number of atoms in the products. This is true according to the Law of Conservation of Mass, which states that the total mass remains constant during a chemical reaction. In other words, matter cannot be created or destroyed in a chemical reaction. In a chemical equation, the reactants are shown on the left and the products are on the right. An arrow in between indicates that a chemical reaction occurs. Finally, the physical state of each compound is designated in parentheses after the chemical formula. Solid, liquid, gas, and aqueous (dissolved in water) are shown as(s,(n,(g), and (aq), respectively.

Science Tutor: Chemistry Name: Mixtures, Solutions, &Compounds: Chemical Equations Date Chemical Equations If a chemical symbol can be thought of as a letter and a chemical formula as a word in the language of chemistry, then a chemical equation is a statement or sentence. A chemical equation is a shorthand way of describing a chemical reaction between two or more substances. A "+ sign means "combines with." An arrow points away from the reactants and toward the products (See page 10), and an arrow means "yields." 2Na + Cl2 â 2NaCl means sodium combines with chlorine to yield sodiumn chloride (salt) Look closely at the equation above. Notice the "2" in front of NaCI on the right and Na on the left. That 2, called a coefficient, is necessary to make this equation balance. Remember Antoine Lavoisier? (Page 15) Matter is neither created nor destroyed in a chemical reaction. The same number of each kind of atom must be on both sides of a chemical equation. Because chlorine only exists as a molecule consisting of two chlorine atoms, it requires two atoms of sodium to yield two molecules of salt (NaCI). This illustrates another important law stated clearly by the French chemist Joseph-Louis Proust in 1799. Chemical compounds always combine in certain specific fixed proportions. Wherever sodium and chlorine combine, two atoms of sodium will be necessary to react with one molecule of gaseous chlorine. 1 . For the equation 2Mg + O2â 2MgO + energy: A. List the reactant or reactants 2Hato B. List the product or products C. How many atoms of magnesium does it take to combine with one molecule of oxygen? D. How many molecules of magnesium oxide are produced in this reaction? 2. Hydrogen can combine with oxygen to produce water. We could write the equation like this: H2 + O2 â H2O. But this equation is unbalanced! Rewrite this equation with the correct coefficients so that an atom of oxygen doesn't disappear! (Be careful. If you add a coefficient to one side you may have to adjust the other. Count all the atoms.) 3. Now that you have the idea, balance the following equations: A, Pho, â PbO + 02 C. Ca + H2O â Ca(OH)2 + H2 How is following a recipe to mix up a batch of biscuits (or any other food item) similar to Proust's law for chemical reactions? 4. OMark Twain Media, Inc., Publishers 17

A. Write a net ionic equation for all chemical reactions below.(Hint: it is possible for the net ionic equation to be the same asthe molecular equation. A complex ion that is in solution ismolecular in nature because units are coordinate covalently bondedtogether.)

1. Cu (s) + 4HNO3 (aq) --> Cu(NO3)2 (aq) + 2NO2 (g) + 2H2O(l)

2. Cu(NO3)2 (aq) + 2NaOH (aq) --> Cu(OH)2 (s) + 2NaNo3(aq)

3. Cu(OH)2 (s) --> CuO (s) + H2O (l)

4. CuO (s) + H2SO4 (aq) --> CuSO4 (aq) + H2O (l)

5. CuSO4 (aq) + Zn (s) --> Cu (s) + ZnSO4 (aq)

6. Zn (s) + H2SO4 (aq) --> ZnSO4 (aq) + H2 (g)

7. Zn (s) + 2HCl (aq) --> ZnCl2 (aq) + H2 (g)

B. Balance the following equations. Write each in both themolecular and net ionic form. Idenfity each reaction as anacid-base reaction, a precipitation reaction, anoxidation-reduction reaction, or as a combination of more than oneof these types.

1. ___Pb(NO3)2 (aq) + ____ NaCl (aq) --> _____PbCl2 (s) +_____NaNO3 (aq)

a) Molecular Equation:

b) Net Ionic Equation:

c) Reaction Type:

2. ___HNO3 (aq) + _____Zn(OH)2 (s) --> ____Zn(NO3)2 (aq) +____H2O (l)

a) Molecular Equation:

b) Net Ionic Equation:

c) Reaction Type:

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CHEM 1021 Lecture Notes - Lecture 5: Iron(Iii) Oxide, Aluminium Oxide, Reagent

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