CHAPTER 11 Stoichiometry 11.1 Analyzing a Chemical Reaction

2 Chemical equations tell stories… 2CO(g) + O 2 (g) → 2CO 2 (g)

Analyzing a Chemical Reaction Chemical equations tell stories… … and stories can be put into different categories Synthesis / Decomposition Single / Double replacement Precipitate reaction Polymerization reaction 2CO(g) + O 2 (g) → 2CO 2 (g)

Analyzing a Chemical Reaction Chemical equations tell stories… But what exactly do they tell us? 2CO(g) + O 2 (g) 2CO 2 (g) They tell uswhat compounds we start with: Carbon monoxide (CO) gas Oxygen (O 2 ) gas what compounds are formed: Carbon dioxide (CO 2 ) gas

Analyzing a Chemical Reaction Chemical equations tell stories… What else do they tell us? 2CO(g) + O 2 (g) 2CO 2 (g)

Analyzing a Chemical Reaction Chemical equations tell stories… What else do they tell us? 2CO(g) + O 2 (g) 2CO 2 (g) 2 CO molecules2 CO 2 molecules1 O 2 molecules They tell us how much of each compound is involved

Analyzing a Chemical Reaction Chemical equations tell stories… What else do they tell us? 2CO(g) + O 2 (g) 2CO 2 (g) stoichiometry: the study of the amounts of substances involved in a chemical reaction. 2 CO molecules2 CO 2 molecules1 O 2 molecules They tell us how much of each compound is involved

Analyzing a Chemical Reaction 2CO(g) + O 2 (g) 2CO 2 (g) 2 CO molecules 2 dozen CO molecules 1 O 2 molecules 1 dozen O 2 molecules 2 CO 2 molecules 2 dozen CO 2 molecules

Analyzing a Chemical Reaction 2CO(g) + O 2 (g) 2CO 2 (g) 2 CO molecules 2 dozen CO molecules 2 moles CO molecules 1 O 2 molecules 1 dozen O 2 molecules 1 mole O 2 molecules 2 CO 2 molecules 2 dozen CO 2 molecules 2 moles CO 2 molecules

Analyzing a Chemical Reaction 2CO(g) + O 2 (g) 2CO 2 (g) 2 CO molecules 2 dozen CO molecules 2 moles CO molecules 2 x (6.023 x ) CO molecules 1 O 2 molecules 1 dozen O 2 molecules 1 mole O 2 molecules (1 x) x O 2 molecules 2 CO 2 molecules 2 dozen CO 2 molecules 2 moles CO 2 molecules 2 x (6.023 x ) CO 2 molecules

Analyzing a Chemical Reaction 2CO(g) + O 2 (g) 2CO 2 (g) 2 moles CO molecules 1 mole O 2 molecules 2 moles CO 2 molecules Number of moles is not conserved Is that okay? ≠ +

Analyzing a Chemical Reaction 2CO(g) + O 2 (g) 2CO 2 (g) 2 moles CO molecules 1 mole O 2 molecules 2 moles CO 2 molecules Number of moles is not conserved Is that okay? Yes, as long as the chemical equation is balanced! ≠ +

Analyzing a Chemical Reaction 2CO(g) + O 2 (g) 2CO 2 (g) 2 C atoms 2 O atoms 2 C atoms 4 O atoms Number of atoms is conserved This chemical equation is balanced = =+

Analyzing a Chemical Reaction 2CO(g) + O 2 (g) 2CO 2 (g) 2 moles CO molecules 1 mole O 2 molecules 2 moles CO 2 molecules This chemical equation is balanced The coefficients are correct Coefficients

Analyzing a Chemical Reaction 2CO(g) + O 2 (g) 2CO 2 (g) 2 moles CO molecules 1 mole O 2 molecules 2 moles CO 2 molecules This chemical equation is balanced The coefficients are correct Coefficients These are important!

Analyzing a Chemical Reaction Coefficients are important 1 bag cake mix + 3 eggs + ¼ cup oil + 1 cup water 1 batch cupcakes

Analyzing a Chemical Reaction Coefficients are important + 3 eggs + ¼ cup oil + 1 cup water 1 batch cupcakes 1 bag cake mix I need ¼ cup of oil to make 1 batch of cupcakes

Analyzing a Chemical Reaction Coefficients are important + 3 eggs + ¼ cup oil + 1 cup water 1 batch cupcakes 1 bag cake mix Write as a ratio:

Analyzing a Chemical Reaction Coefficients are important + 3 eggs + ¼ cup oil + 1 cup water 1 batch cupcakes 1 bag cake mix I need 1 cup of oil to make 4 batches of cupcakes

Analyzing a Chemical Reaction Write as a ratio: Coefficients are important + 3 eggs + ¼ cup oil + 1 cup water 1 batch cupcakes 1 bag cake mix

Analyzing a Chemical Reaction Coefficients are important C 6 H 12 O 6 (aq) 2C 2 H 5 OH(aq) + 2CO 2 (g) Fermentation of sugar (glucose) into alcohol: 1 mole glucose 2 moles ethanol 2 moles carbon dioxide

Analyzing a Chemical Reaction Coefficients are important C 6 H 12 O 6 (aq) 2C 2 H 5 OH(aq) + 2CO 2 (g) Fermentation of sugar (glucose) into alcohol: 1 mole glucose 2 moles ethanol 2 moles carbon dioxide 1 moles 3 moles glucose will yield 2 moles 6 moles ethanol/ carbon dioxide x 3

Analyzing a Chemical Reaction Coefficients are important C 6 H 12 O 6 (aq) 2C 2 H 5 OH(aq) + 2CO 2 (g) Fermentation of sugar (glucose) into alcohol: 1 mole glucose 2 moles ethanol 2 moles carbon dioxide 1 moles 3 moles 7.5 moles glucose will yield 2 moles 6 moles 15 moles ethanol/ carbon dioxide x 7.5 x 3

Analyzing a Chemical Reaction Coefficients are important C 6 H 12 O 6 (aq) 2C 2 H 5 OH(aq) + 2CO 2 (g) Fermentation of sugar (glucose) into alcohol: 1 mole glucose 2 moles ethanol 2 moles carbon dioxide 7.5C 6 H 12 O 6 (aq) 15C 2 H 5 OH(aq) + 15CO 2 (g) 7.5 moles glucose 15 moles ethanol 15 moles carbon dioxide You MUST multiply all the coefficients by the same number

Analyzing a Chemical Reaction C 6 H 12 O 6 (aq) 2C 2 H 5 OH(aq) + 2CO 2 (g) Fermentation of sugar (glucose) into alcohol: 1 mole glucose 2 moles ethanol 2 moles carbon dioxide Write as a ratio: These are stoichiometric equivalents

Analyzing a Chemical Reaction C 6 H 12 O 6 (aq) 2C 2 H 5 OH(aq) + 2CO 2 (g) Fermentation of sugar (glucose) into alcohol: 1 mole glucose 2 moles ethanol 2 moles carbon dioxide Write as a ratio: mole ratio: a ratio comparison between substances in a balanced equation. It is obtained from the coefficients in the balanced equation.

Analyzing a Chemical Reaction C 6 H 12 O 6 (aq) 2C 2 H 5 OH(aq) + 2CO 2 (g) Fermentation of sugar (glucose) into alcohol: 1 mole glucose 2 moles ethanol 2 moles carbon dioxide mole ratios for this chemical equation Mole ratios

Analyzing a Chemical Reaction CO(g) + 2H 2 (g) CH 3 OH(l) Mole ratios Consider the following equation: Compare the reactant CO to the product CH 3 OH. carbon monoxide hydrogenmethanol

Analyzing a Chemical Reaction CO(g) + 2H 2 (g) CH 3 OH(l) Mole ratios Consider the following equation: carbon monoxide hydrogenmethanol Compare the reactant CO to the product CH 3 OH.

Analyzing a Chemical Reaction CO(g) + 2H 2 (g) CH 3 OH(l) Mole ratios Consider the following equation: carbon monoxide hydrogenmethanol If the reaction produces 5 moles of CH 3 OH, how many moles of H 2 are consumed?

Analyzing a Chemical Reaction CO(g) + 2H 2 (g) CH 3 OH(l) Mole ratios Consider the following equation: carbon monoxide hydrogenmethanol If the reaction produces 5 moles of CH 3 OH, how many moles of H 2 are consumed? Asked: moles of H 2 Given: moles of CH 3 OH

Analyzing a Chemical Reaction CO(g) + 2H 2 (g) CH 3 OH(l) Mole ratios Consider the following equation: carbon monoxide hydrogenmethanol If the reaction produces 5 moles of CH 3 OH, how many moles of H 2 are consumed? Asked: moles of H 2 Given: moles of CH 3 OH Write the mole ratio between H 2 and CH 3 OH Write moles of H 2 (asked) “on top”

Analyzing a Chemical Reaction CO(g) + 2H 2 (g) CH 3 OH(l) Mole ratios Consider the following equation: carbon monoxide hydrogenmethanol If the reaction produces 5 moles of CH 3 OH, how many moles of H 2 are consumed? “on top” Asked: moles of H 2 Write the mole ratio between H 2 and CH 3 OH Write moles of H 2 (asked) “on top”

Analyzing a Chemical Reaction CO(g) + 2H 2 (g) CH 3 OH(l) Mole ratios Consider the following equation: carbon monoxide hydrogenmethanol If the reaction produces 5 moles of CH 3 OH, how many moles of H 2 are consumed? Given: moles of CH 3 OH

Analyzing a Chemical Reaction CO(g) + 2H 2 (g) CH 3 OH(l) Mole ratios Consider the following equation: carbon monoxide hydrogenmethanol If the reaction produces 5 moles of CH 3 OH, how many moles of H 2 are consumed? Asked: moles of H 2

Analyzing a Chemical Reaction A mixture of aluminum metal and chlorine gas reacts to form aluminum chloride (AlCl 3 ): 2Al(s) + 3Cl 2 (g) → 2AlCl 3 (s). How many moles of aluminum chloride will form when 5 moles of chlorine gas react with excess aluminum metal?

Analyzing a Chemical Reaction A mixture of aluminum metal and chlorine gas reacts to form aluminum chloride (AlCl 3 ): 2Al(s) + 3Cl 2 (g) → 2AlCl 3 (s). How many moles of aluminum chloride will form when 5 moles of chlorine gas react with excess aluminum metal? Asked: moles AlCl 3 Given: moles Cl 2

Analyzing a Chemical Reaction A mixture of aluminum metal and chlorine gas reacts to form aluminum chloride (AlCl 3 ): 2Al(s) + 3Cl 2 (g) → 2AlCl 3 (s). How many moles of aluminum chloride will form when 5 moles of chlorine gas react with excess aluminum metal? Asked: moles AlCl 3 Given: moles Cl 2 Write the mole ratio between AlCl 3 and Cl 3 Write moles of AlCl 3 (asked) “on top”

Analyzing a Chemical Reaction A mixture of aluminum metal and chlorine gas reacts to form aluminum chloride (AlCl 3 ): 2Al(s) + 3Cl 2 (g) → 2AlCl 3 (s). How many moles of aluminum chloride will form when 5 moles of chlorine gas react with excess aluminum metal? Asked: moles AlCl 3 Given: moles Cl 2 “on top” Write the mole ratio between AlCl 3 and Cl 3 Write moles of AlCl 3 (asked) “on top”

Analyzing a Chemical Reaction A mixture of aluminum metal and chlorine gas reacts to form aluminum chloride (AlCl 3 ): 2Al(s) + 3Cl 2 (g) → 2AlCl 3 (s). How many moles of aluminum chloride will form when 5 moles of chlorine gas react with excess aluminum metal? Asked: moles AlCl 3 Given: moles Cl 2

Analyzing a Chemical Reaction A mixture of aluminum metal and chlorine gas reacts to form aluminum chloride (AlCl 3 ): 2Al(s) + 3Cl 2 (g) → 2AlCl 3 (s). How many moles of aluminum chloride will form when 5 moles of chlorine gas react with excess aluminum metal? Asked: moles AlCl 3 Given: moles Cl 2 units cancel out

Analyzing a Chemical Reaction A mixture of aluminum metal and chlorine gas reacts to form aluminum chloride (AlCl 3 ): 2Al(s) + 3Cl 2 (g) → 2AlCl 3 (s). How many moles of aluminum chloride will form when 5 moles of chlorine gas react with excess aluminum metal? Asked: moles AlCl 3 Given: moles Cl 2 units cancel out

Analyzing a Chemical Reaction A mixture of aluminum metal and chlorine gas reacts to form aluminum chloride (AlCl 3 ): 2Al(s) + 3Cl 2 (g) → 2AlCl 3 (s). How many moles of aluminum chloride will form when 5 moles of chlorine gas react with excess aluminum metal? Asked: moles AlCl 3 Given: moles Cl 2 Answer: 3.3 moles of AlCl 3 are produced.

Analyzing a Chemical Reaction There is no scale that measures in moles! How do you convert from moles to grams? The mass of 1 mole of Al is not the same as the mass of 1 mole of Cl 2. How do you convert from grams of Al to grams of Cl 2 ?

Analyzing a Chemical Reaction There is no scale that measures in moles! How do you convert from moles to grams? The mass of 1 mole of Al is not the same as the mass of 1 mole of Cl 2. How do you convert from grams of Al to grams of Cl 2 ? By using the molar mass (g/mole) By using the molar mass (g/mole) and mole ratios

Analyzing a Chemical Reaction Process for calculating grams from grams given

Analyzing a Chemical Reaction If 45.0 g of calcium carbonate (CaCO 3 ) decomposes in the reaction CaCO 3 (s) → CaO(s) + CO 2 (g), how many grams of CO 2 are produced? Calcium carbonate (CaCO 3 ) is present in rocks, eggshells and most seashells. CaCO 3 decomposes when it is heated.

Analyzing a Chemical Reaction If 45.0 g of calcium carbonate (CaCO 3 ) decomposes in the reaction CaCO 3 (s) → CaO(s) + CO 2 (g), how many grams of CO 2 are produced? Asked: grams of CO 2 Given: grams of CaCO 3 Relationships: mole ratios molar mass of CaCO 3 = ( x 3) = g/mole molar mass of CO 2 = ( x 2) = g/mole Strategy:

Analyzing a Chemical Reaction If 45.0 g of calcium carbonate (CaCO 3 ) decomposes in the reaction CaCO 3 (s) → CaO(s) + CO 2 (g), how many grams of CO 2 are produced? Asked: grams of CO 2 Given: grams of CaCO 3 Relationships: mole ratios, molar mass of CaCO 3 = g/mole molar mass of CO 2 = g/mole 45.0 g CaCO 3

Analyzing a Chemical Reaction If 45.0 g of calcium carbonate (CaCO 3 ) decomposes in the reaction CaCO 3 (s) → CaO(s) + CO 2 (g), how many grams of CO 2 are produced? Asked: grams of CO 2 Given: grams of CaCO 3 Relationships: mole ratios, molar mass of CaCO 3 = g/mole molar mass of CO 2 = g/mole 45.0 g CaCO moles CaCO 3

Analyzing a Chemical Reaction If 45.0 g of calcium carbonate (CaCO 3 ) decomposes in the reaction CaCO 3 (s) → CaO(s) + CO 2 (g), how many grams of CO 2 are produced? Asked: grams of CO 2 Given: grams of CaCO 3 Relationships: mole ratios, molar mass of CaCO 3 = g/mole molar mass of CO 2 = g/mole 0.45 moles CaCO 3

Analyzing a Chemical Reaction If 45.0 g of calcium carbonate (CaCO 3 ) decomposes in the reaction CaCO 3 (s) → CaO(s) + CO 2 (g), how many grams of CO 2 are produced? Asked: grams of CO 2 Given: grams of CaCO 3 Relationships: mole ratios, molar mass of CaCO 3 = g/mole molar mass of CO 2 = g/mole 0.45 moles CaCO moles CO 2

Analyzing a Chemical Reaction If 45.0 g of calcium carbonate (CaCO 3 ) decomposes in the reaction CaCO 3 (s) → CaO(s) + CO 2 (g), how many grams of CO 2 are produced? Asked: grams of CO 2 Given: grams of CaCO 3 Relationships: mole ratios, molar mass of CaCO 3 = g/mole molar mass of CO 2 = g/mole 0.45 moles CO 2

Analyzing a Chemical Reaction If 45.0 g of calcium carbonate (CaCO 3 ) decomposes in the reaction CaCO 3 (s) → CaO(s) + CO 2 (g), how many grams of CO 2 are produced? Asked: grams of CO 2 Given: grams of CaCO 3 Relationships: mole ratios, molar mass of CaCO 3 = g/mole molar mass of CO 2 = g/mole 0.45 moles CO g CO 2

Analyzing a Chemical Reaction If 45.0 g of calcium carbonate (CaCO 3 ) decomposes in the reaction CaCO 3 (s) → CaO(s) + CO 2 (g), how many grams of CO 2 are produced? Asked: grams of CO 2 Given: grams of CaCO 3 Relationships: mole ratios, molar mass of CaCO 3 = g/mole molar mass of CO 2 = g/mole 0.45 moles CO g CO 2 45 g CaCO moles CaCO 3 Answer: 19.8 g of CO 2 are produced.

Analyzing a Chemical Reaction C 6 H 12 O 6 (aq) 2C 2 H 5 OH(aq) + 2CO 2 (g) 1 mole glucose 2 moles ethanol 2 moles carbon dioxide These are stoichiometric equivalents Mole ratios: