Chemistry Ch. 7

• Climate Change and the Combustion of Fossil Fuels
• Physical and Chemical Changes
• In a chemical reaction, the limiting reactant is the reactant that is consumed first.
• Theoretical yield is the maximum amount of product that can be obtained from a chemical reaction.
• Percent yield is the actual yield as a percentage of the theoretical yield.
• Reactant in excess is when the amount of reactant is more than the amount of product.
• Writing and Balancing Chemical Equations
• Reaction Stoichiometry: How Much Carbon Dioxide
• Stoichiometric Relationships: Limiting Reactant, Theoretical Yield, Percent Yield, and Reactant in Excess
• The temperature of Earth is maintained by
• The amount of CO2 in the atmosphere effects the temperature on Earth
• There are natural (volcano) and man-made (car exhaust) sources of CO2.
• Which source is driving this change in the atmosphere?
• A property is a characteristic useful for identifying a substance or object, including size, color, and temperature, as well as chemical composition and chemical reactivity.
• Changes in properties can be physical or chemical.
• A physical change is a change that does not affect the chemical makeup of a substance or object.
• A chemical change is a change in the chemical makeup of a substance.
• Chemical equations show a reaction.
• Reactants (state) → Products (state)
• According to law of conservation of mass we must have the same # of atoms of a specific element on both sides of our equation.
• In a chemical equation, elements that exist as diatomic molecules must be written as H2 and O2 rather than as H and O.
• When balancing a chemical equation, begin with elements that appear in only one compound or formula on each side of the equation.
• Subscripts in chemical formulas cannot be changed.
• If a polyatomic ion appears on both sides of an equation, it is treated as a single unit.
• To check the equation to make sure the # and kinds of atoms on both sides of the equation are the same, add the numbers of atoms of each element on both sides of the equation and make sure they are equal.
• To make sure the coefficients are reduced to their lowest whole-number values, add the numbers of atoms of each element on both sides of the equation and make sure they are equal.
• Fossil fuel combustion reaction: 2 C8H18 (l) + 25 O2 (g)→ 16 CO2 (g) +18 H2O (g).
• Coefficients in a chemical equation show the ratio of moles of substance.
• In the reaction 2 C8H18 (l) + 25 O2 (g)→ 16 CO2 (g) +18 H2O (g), 2 moles C8H18 :16 moles CO2.
• Stoichiometric relationships include the concepts of limiting reactant, theoretical yield, percent yield, and reactant in excess.
• The relationship between reactants and products can be represented by the equation 1 crust + 5 ounces sauce + 2 cups cheese → 1 pizza.
• Starting with 4 crusts, 4 pizzas can be made.
• Starting with 10 cups cheese, 5 pizzas can be made.
• Starting with 15 ounces sauce, 3 pizzas can be made.
• The limiting reagent in the equation 1 crust + 5 ounces sauce + 2 cups cheese → 1 pizza is the sauce, which is the smallest amount of product.
• Theoretical yield is the maximum amount of product that can be formed based on the limiting reagent.
• Actual yield is the amount of product actually produced.
• Percent yield is the percentage of actual yield to theoretical yield.
• The relationship between reactants and products can also be represented by the equation 2 C8H18 (l) + 25 O2 (g)→ 16 CO2 (g) +18 H2O (g).
• If we have 5 molecules C8H18 and 25 molecules O2, the C8H18 molecules are the limiting reactants, as they are the smallest amount of product.