CHAPTER 4: CHANGES IN MATTER

(1) WHAT ARE CHANGES IN MATTER?

(Recall: characteristic property: enable us to identify a substance for example:

DensityColorSizeTextureHardnessSoftnessmelting pointboiling pointfreezing pointFlammabilityreaction with acids/oxygenSolubilityMalleabilityductilitythermal conductivityelectric conductivity

Three types of changes in matter:

1. Physical change: the substance's characteristic properties, atoms or molecules, and its nature do not change; ex. cutting, filtering, crushing, changes in state.

2. Chemical change: the nature of a sub changes since it reacts with another compound to form a something new as chemical bonds are rearranged; ex. burning paper, rusting metal or browning of a cut fruit (oxidation).

3. Nuclear transformation: A deeper change which occurs at the nuclear level of the atom; when atoms split to form new elements (ex. fission) a tremendous amount of energy is released; usually the nucleus is bombarded by a particle at a very high speed.

Nuclear fission

(2) CHEMICAL CHANGES

- Bonds of reactants are broken and reformed to give new products.- Reactants and products are different chemicals with different characteristic properties.-The graph below indicates a chemical change since the quantity of products increases as the quantity of reactants (reagents) decreases.

Five signs indicating a chemical reaction:

(1) a gas is released(2) heat is absorbed or released, (3) light appears(4) there is a change in color(5) a precipitate (a solid in solution) is formed

Chemical change = chemical reaction

A chemical equation demonstrates what happens during a reaction and how the reactants give way to the products.

2.1 THE LAW OF CONSERVATION OF MASS

-During a chemical reaction nothing is lost or created (According to Lavoisiere) the atoms involved don't change only the bonds are rearranged.

-The total mass of the reactants is always = the total mass of the products (which is handy for calculations and stoichiometry)

2.2 BALANCING CHEMICAL EQUATIONS

-Number of atoms on one side of a chemical equation equal atoms on the other side of the equation

-An equation is balanced by adding a coefficient (number) in front of a substance

Five rules must be followed:

(1) Coefficients must always be whole numbers (You may use decimals to help you balance, but then they must be turned into whole numbers)

(2) Coefficients must be as small as possible

(3) Substances in the equation cannot be changed

(4) Never change the subscript (a subscript is, for example, the 2 in H2O)

(5) When you're done always make sure the number of atoms on both sides of the equation balance

2.3 STOICHIOMETRY

When using stoichiometry, information about reactants and products is determined by using the balanced equation involved

Example:

During photosynthesis the sun's energy is needed in order to produce glucose.

CO2 + H2O + energy C6H12O6 + O2 Q1. How many moles of water would be needed to produce 3.8 moles of glucose?

Steps: (1) Balance the equation(2) Set up a box under the equation which gives the moles and masses of the products and

reactants. This will be handy to work out problems.

moles 6 6 1 6mass (g) 264.06 108.12 180.18 192.00

6CO2 + 6H2O + energy C6H12O6 + 6O2

(3) Set up a proportion by using information from the equation combined with information from the question. Cross multiply to find the answer.6 moles H2O = 1 mol C6H12O6 (6 moles H2O) (3.8 mol C6H12O6) = 22.8 mole H2O ? moles H2O = 3.8 mol C6H12O6 1 mol C6H12O6

Q2. How many moles of oxygen would result if you started with 100g CO2?From the equation: 6 moles O2 = 264.06g CO2 (6 moles O2) ( 100g CO2) = 2.27 moles O2 From the question: ? moles O2 = 100g CO2 264.06g CO2

Additional reference: Toolbox p.53

STOICHIOMETRY PRACTICE (answer in your Tandem) 1. Hydrogen peroxide (H2O2) breaks down according to the following reaction: H2O2 --> H2O + O2

a. In an experiment, a student adds 0.9 moles of hydrogen peroxide to a test tube. If it completely decomposes how many grams of oxygen will be produced?b. How many moles of hydrogen peroxide are needed to produce 8.7 moles of water?c. If 450g H2O2 is decomposed, how many grams of water are produced?

2. AlCl3 + NaOH --> NaAlO2 + NaCl + H2O a. For every 1.0 gram of NaCl produced what mass of water will be obtained?b. How many moles of water will be obtained if the amount of NaCl is doubled?c. How many moles of NaAlO2 (sodium aluminate) are there in 5g?

3. HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

a. 0.0020kg HCl will yield how many grams H2O?b. What is the total mass of the reactants involved?c. How many grams of base is needed to produce 3.6 moles of salt?

4. C6H12O6 → CH3CHOHCOOH + C2H5OH + CO2 During this fermentation reaction glucose yields lactic acid (CH3CHOHCOOH), ethanol (C2H5OH), and carbon dioxide. a. 1g glucose yields how many moles of lactic acid?b. How many moles are there in 1g glucose?c. What mass of ethanol can be produced with 4kg glucose?d. How many grams reactants are needed if 50g lactic acid is produced during this reaction? e. Why is the mass of glucose greater than the mass of ethanol?f. The technician wants to make 10g lactic acid. If she has 2 moles glucose, does she have enough glucose to make the 10g lactic acid? Justify your answer. g. What is unusual about the formula of lactic acid?