3.1 Chemical measurements, conservation of mass, and the quantitative interpretation of chemical equations

• The law of conservation of mass states that matter cannot be created or destroyed
• A mole ratio is the ratio of the number of moles of reactants and products in a balanced chemical equation.
• What does quantitative chemistry study?

  Quantities in chemical reactions
• In the reaction $CH_{4} +$$2O_{2} \rightarrow CO_{2} +$$2H_{2}O$, the reactants are $CH_{4}$ and $O_{2}$.


  True
• What is a mole ratio in stoichiometry?

  Ratio of moles of reactants and products
• A mole ratio is always expressed as a fraction.


  True
• In the reaction $N_{2} +$$3H_{2} \rightarrow 2NH_{3}$, how many moles of $H_{2}$ are needed if you start with 2 moles of $N_{2}$?


  6 moles
• In the reaction 2H_{2} + O_{2} \rightarrow 2H_{2}O</latex>, if you have 4 moles of $H_{2}$, how many moles of $O_{2}$ are needed?


  2 moles
• In the reaction $CH_{4} +$$2O_{2} \rightarrow CO_{2} +$$2H_{2}O$, what are the products?


  $CO_{2}$ and $H_{2}O$
• Steps to balance a chemical equation

  1️⃣ Identify the reactants and products

  2️⃣ Count the atoms of each element on both sides

  3️⃣ Add coefficients as needed to balance the atoms

  4️⃣ Double-check that all elements are balanced
• Balancing a chemical equation ensures the number of atoms of each element is equal on both sides.


  True
• What is the mole ratio of $N_{2}$ to $NH_{3}$ in the reaction $N_{2} +$$3H_{2} \rightarrow 2NH_{3}$?


  $1:2$
• Chemical measurements are a fundamental aspect of quantitative chemistry.
• A closed system is one where no matter enters or leaves.
• In the equation H_{2} + O_{2} \rightarrow H_{2}O</latex>, the oxygen needs to be balanced.
• Match the mole ratios from the equation $N_{2} +$$3H_{2} \rightarrow 2NH_{3}$:


  N2 to H2 ↔️ 1:3

  N2 to NH3 ↔️ 1:2

  H2 to NH3 ↔️ 3:2
• A mole quantity refers to the amount of a substance expressed in moles.
• Steps to solve quantitative chemistry problems related to reactions

  1️⃣ Write the balanced chemical equation

  2️⃣ Identify the known and unknown quantities

  3️⃣ Use mole ratios to convert

  4️⃣ Calculate the required quantity
• What is the primary focus of chemical measurements?

  Quantitative analysis
• In a closed system, the total mass of reactants equals the total mass of products according to the law of conservation of mass.


  True
• The law of conservation of mass applies to reactions in a closed system.
• What is the final balanced equation for the reaction $CH_{4} +$$O_{2} \rightarrow CO_{2} +$$H_{2}O$?


  $CH_{4} +$$2O_{2} \rightarrow CO_{2} +$$2H_{2}O$
• Match the substances in the reaction N_{2} + 3H_{2} \rightarrow 2NH_{3}</latex> with their mole ratios:

  $N_{2}$ ↔️ $1:3$

  $H_{2}$ ↔️ $3:2$

  $NH_{3}$ ↔️ $1:2$
• Why are chemical measurements crucial in chemistry?

  Understanding and predicting chemical behavior
• What does the law of conservation of mass state?

  Total mass remains constant
• Steps to balance a chemical equation

  1️⃣ List all elements present

  2️⃣ Count atoms of each element

  3️⃣ Use coefficients to balance atoms

  4️⃣ Double-check that all elements are balanced
• To determine mole ratios, the first step is to write the balanced chemical equation.
• What is stoichiometry used for in chemistry?

  Calculating amounts of substances
• Stoichiometry is based on the law of conservation of mass.

  True
• The mole ratio in the reaction $2H_{2} +$$O_{2} \rightarrow 2H_{2}O$ is 2H_{2}:$1O_{2}$.