4.3 Representations of Reactions

• Balancing chemical equations ensures mass is neither created nor destroyed during a reaction.


  True
• What do molecular diagrams help to understand?

  Molecular structure and bonding
• What is a balanced chemical equation?

  Atoms balanced on both sides
• The molar ratio of H₂ to O₂ in the reaction 2H₂ + O₂ → 2H₂O is 2:1
• A balanced chemical equation must adhere to the law of conservation of mass.


  True
• What is an energy diagram used to visualize?

  Energy changes in reactions
• Balancing a chemical equation ensures that the number of atoms for each element remains constant.


  True
• In stoichiometry, molar ratios are derived from the coefficients of a balanced chemical equation
• Arrange the steps in deriving molar ratios from a balanced chemical equation.

  1️⃣ Identify coefficients in the balanced equation

  2️⃣ Determine the relationship between moles of reactants and products

  3️⃣ Express the relationship as a ratio
• What is the molar ratio of O₂ to H₂O in the reaction 2H₂ + O₂ → 2H₂O?

  1:2
• Match the type of molecular diagram with its key feature:

  Structural Formulas ↔️ Shows bond types and connectivity

  Lewis Structures ↔️ Highlights electron distribution

  Ball-and-Stick Models ↔️ Depicts 3D atomic arrangement

  Space-Filling Models ↔️ Illustrates molecular shape
• Which type of reaction absorbs energy from the surroundings?

  Endothermic
• What is the molar ratio of H₂ to O₂ in the reaction 2H₂ + O₂ → 2H₂O?

  2 : 1
• Arrange the following types of molecular diagrams based on their ability to depict spatial arrangements:

  1️⃣ Lewis Structures

  2️⃣ Ball-and-Stick Models

  3️⃣ Space-Filling Models
• Ball-and-stick models visualize 3D molecular geometry and bond angles
• The activation energy in an energy diagram is the energy required to start the reaction
• Give an example of an exothermic reaction.

  Combustion
• What does the plateau in a reaction progress curve indicate?

  Equilibrium
• An example of an exothermic reaction is combustion
• The molar ratio of O₂ to H₂O in the reaction 2H₂ + O₂ → 2H₂O is 1:2
• The molar ratio of H₂ to O₂ in the reaction 2H₂ + O₂ → 2H₂O is 1 : 2.

  False
• What does a Lewis structure depict in molecular bonding?

  Covalent bonding
• What does an energy diagram plot against the reaction progress?

  Energy
• Describe the general shape of a reaction progress curve.

  1️⃣ Reactant concentration is high, product concentration is low.

  2️⃣ Reactant concentration decreases, product concentration increases.

  3️⃣ The curve reaches a plateau at equilibrium.
• Match the type of molecular diagram with its key feature:

  Lewis Structures ↔️ Highlights electron distribution

  Ball-and-Stick Models ↔️ Depicts 3D structure

  Space-Filling Models ↔️ Illustrates molecular shape
• Space-filling models use spheres scaled to van der Waals radii to illustrate molecular shape.

  True
• Exothermic reactions have a positive enthalpy change (ΔH > 0).

  False
• An endothermic reaction absorbs energy
• In a reaction progress curve, the steepness of the slope indicates the reaction rate