5.4.1 Reacting Masses

• Stoichiometry is the study of quantitative relationships between reactants and products in chemical reactions
• The balanced chemical equation $2H_{2} +$$O_{2} \rightarrow 2H_{2}O$ shows a stoichiometric ratio of 2:1:2 between hydrogen, oxygen, and water.
• Stoichiometry tells us that two moles of hydrogen react with one mole of oxygen to produce two moles of water
• Understanding reacting masses is crucial for calculating the exact amounts of reactants needed in a chemical reaction.
• For the reaction $2H_{2} +$$O_{2} \rightarrow 2H_{2}O$, the reacting masses can be calculated using the molar masses of hydrogen and oxygen
• In a stoichiometric reaction, the reacting masses are in the exact proportions required by the balanced chemical equation
• Understanding reacting masses is crucial because it allows us to calculate the exact amounts of reactants needed to produce a specific amount of product
• What is the main difference between stoichiometric and non-stoichiometric reactions?

  Exact vs. non-exact proportions
• In a stoichiometric reaction, all reactants are used up completely
• Stoichiometry allows us to calculate the exact amounts of reactants needed to produce a specific amount of product
• Match the reaction type with its description:

  Stoichiometric ↔️ Exact proportions

  Non-stoichiometric ↔️ Non-exact proportions
• Why is stoichiometry important in chemistry?

  For efficient and safe experiments
• In a non-stoichiometric reaction, there are no leftover reactants

  False
• What is molar mass expressed in?

  Grams per mole
• Molar mass represents the total mass of all the atoms in one molecule of the substance
• What do stoichiometric ratios show in a chemical equation?

  Molar relationships
• Steps to balance a chemical equation:

  1️⃣ Count atoms of each element on both sides

  2️⃣ Balance elements by adjusting coefficients

  3️⃣ Check to ensure equal atoms on both sides
• The balanced equation for $H_{2} +$$O_{2} \rightarrow H_{2}O$ is $2H_{2} +$$O_{2} \rightarrow 2H_{2}O$
• What are reacting masses used to calculate in a chemical reaction?

  Amounts of reactants and products
• In a non-stoichiometric reaction, some reactants are left over.
• Molar mass is crucial for converting between mass and moles
• What is the unit for molar mass?

  grams per mole
• Molar mass is the mass of one mole of a substance.
• What is the molar mass of water ($H_{2}O$)?


  18.016 g/mol
• 18.016 grams of water contains one mole of water molecules.
• Steps to balance a chemical equation

  1️⃣ Count atoms of each element on both sides

  2️⃣ Balance elements by adjusting coefficients

  3️⃣ Check to ensure equal atoms on both sides
• In the balanced equation $2H_{2} +$$O_{2} \rightarrow 2H_{2}O$, the coefficient forH_{2}</latex> is 2.
• What is the balanced chemical equation for the reaction $H_{2} +$$O_{2} \rightarrow H_{2}O$?


  $2H_{2} +$$O_{2} \rightarrow 2H_{2}O$
• Stoichiometric ratios show the molar relationships between reactants and products in a chemical reaction.
• What do stoichiometric ratios allow us to calculate in chemical reactions?

  Precise amounts of reactants
• To calculate reacting masses, the first step is to write a balanced chemical equation.
• Steps to calculate reacting masses

  1️⃣ Write balanced equation to determine mole ratios

  2️⃣ Convert known mass to moles using molar mass

  3️⃣ Use mole ratio to find moles of other reactants or products

  4️⃣ Convert moles back to mass using molar mass
• The law of conservation of mass states that mass is neither created nor destroyed in a closed system.
• What is the total mass of reactants in the reaction 2H_{2} + O_{2} \rightarrow 2H_{2}O</latex>?

  36 g
• Match the implication with its description:

  Ensures mass is accounted for in reactions ↔️ Mass is neither created nor destroyed

  Helps in balancing equations ↔️ Same number of atoms on both sides

  Supports predictability in stoichiometry ↔️ Calculations are accurate
• Stoichiometry is the study of quantitative relationships between reactants and products in chemical reactions.
• In the reaction $2H_{2} +$$O_{2} \rightarrow 2H_{2}O$, the reacting masses of hydrogen and oxygen must be in the ratio 1:16.
• Why is molar mass important in calculating reacting masses?

  Converts mass to moles
• Molar mass is the mass of one mole of a substance, expressed in grams per mole
• What is the molar mass of hydrogen ($H$)?


  1.008 g/mol