Chapter 7.1 Notes

Chapter 7.1 Notes

Describing Reaction

Physical VS Chemical Properties

a. Physical vs Chemical Propertiesa. Physical Change – A change that

occurs when some of the properties of a material change, but the substances in the material remain the same.

b. Chemical Change – A change that occurs when a substance reacts and forms on or more new substances.

Physical VS Chemical Properties

i. Signs of a chemical change include color change, temperature change, light produced, gas formed, precipitate formed.

c. When matter undergoes a chemical change, the composition of the matter changes. When matter undergoes a physical change, the composition of the matter remains the same.

Chemical Reactions

a. Chemical Reactionsa. A useful description of a chemical

reaction tells you the substances present before and after the reaction.

b. Reactants – The substances that undergo change and are present before the reaction takes place.

Chemical Reactions

c. Products – The new substances formed as a result of that change and are present after the reaction takes place.

d. A chemical equation is a representation of a chemical reaction in which the reactants and products are expressed as formulas.

e. Reactants Products

Example 1: Burning Charcoal

• Word Equation:Carbon + Oxygen = Carbon Dioxide

• Chemical Formula:C + O2 = CO2

Conservation of Mass

c. Conservation of Massa. The Law of Conservation of Mass

states that mass is neither created nor destroyed in a chemical reaction.

b. Therefore the mass of the products is always equal to the mass of the reactants.

Conservation of Mass

c. While burning charcoal you actually see the charcoal burn and disappear. The same mass of charcoal that appears to have disappeared is actually converted into carbon dioxide gas.

Balancing Equations

d. Balancing Equationsa. In order to show that mass is conserved

during a reaction, a chemical equation must be balanced.

b. Chemical equations can be balanced by changing the coefficients (the numbers that appear before symbols.)

c. When balancing a chemical equations never change the subscripts in the formula.

E. Steps to Balancing a Chemical Formula

e. Steps to Balancing a Chemical Formulaa. Step 1: Count the number of atoms of

each element on each side of the equation.

b. Step 2: change one or more coefficients until the equation is balanced. (Only change the coefficients that need to be changed.)

Ex. 1) Write a balanced equation for the reaction between copper and oxygen to produce copper(II)

and oxide, CuO.

What do you Know? - Reactants: Cu, O2- Product: CuO

What do you need to know?- Balanced Equation

Plan and Solve:- Write a chemical equation with the

reactants on the left side and the product on the right side

- Cu + O2 CuO- Change the coefficient of CuO in

order to balance the number of O atoms.

- Cu + O2 2CuO- Change the coefficient of Cu.- 2Cu + O2 2CuO

Answer:

Ex. 2) Balance the equation H2O2 H2O + O2

What do you Know? - Reactants: H2O2- Product: H2O + O2

What do you need to know?- Balanced Equation

Plan and Solve:- Write a chemical equation with the

reactants on the left side and the product on the right side

- H2O2 H2O + O2

- Change the coefficient of H2O2 and H2O in order to balance the number of H and O atoms.

- 2H2O2 2H2O + O2

Answer:

Ex. 3) Balance the equation Mg + HCl H2 + MgCl2

What do you Know? - Reactants: Mg, HCl- Product: H2, MgCl2

What do you need to know?- Balanced Equation

Plan and Solve:- Write a chemical equation with the

reactants on the left side and the product on the right side

- Mg + HCl H2 + MgCl2

- Change the coefficient of HCl in order to balance the number of H and Cl atoms.

- Mg + 2HCl H2 + MgCl2

Answer:

Counting With Molesf. Counting With Moles

a. A mole is an amount of a substance that contains approximately 6.02 X 1023 particles of that substance. This number is known as Avogadro’s number

b. Because chemical reactions often involve large numbers of small particles, chemists use a counting unit called the mole to measure amounts of a substance.

Molar Mass

g. Molar Massa. Molar mass is the mass of one mole of a

substance. b. In the same way that a dozen eggs has a

different mass than a dozen oranges, a mole of carbon would have a different mass than a mole of sulfur.

c. The molar mass is the same as the atomic mass expressed in grams

Molar Mass

d. For a compound you can calculate the molar mass by adding up the atomic masses of its component atoms, and then expressing the sum in grams.

Ex. 4) Find the molar mass of a molecule of CO2.• One carbon= 12amu• Two Oxygen= 16amu x 2 = 32amu• 12amu+32amu = 44.0 grams.

Mole-Mass Conversion

h. Mole – Mass Conversiona. Once you know the molar mass of a

substance, you can convert moles of that substance into mass, or a mass of that substance into moles.

Ex. 5) Convert 55.0 g of CO2 to moles.

What do you know?44.0 g CO2 = 1 mol CO2

What do you want to know?55.0g CO2 in moles

Plan and Solve:Use a conversion factor.55.0g CO2 X (1mol CO2/44.0g CO2)

Answer: • = 1.25mol CO2

Ex. 6 Convert 144g of H2O to moles

What do you know?• 18g of H2O = 1 mol of H2O

What do you want to know?• How many moles is 144g of

H2O?

Plan and Solve:• Use a conversion factor.• 144g H2O X (1mol H2O/18g H2O)

Answer: • 144g H2O = 8.00 mol H2O