4.1 Introduction for Reactions

• During a chemical reaction, the starting materials are called reactants
• Order the reversibility of physical and chemical changes.

  1️⃣ Physical changes are generally reversible

  2️⃣ Chemical changes are generally irreversible
• Reactants transform into products through the breaking and rearrangement of chemical bonds.
• What type of change is freezing water?

  Physical change
• Where are products listed in a chemical equation?

  Right side
• What happens in a synthesis reaction?

  Two reactants combine
• In a decomposition reaction, a single reactant breaks down into two or more products
• What happens to ions in a double displacement reaction?

  They exchange
• Balancing chemical equations ensures the number of atoms is the same on both sides of the equation.


  True
• The reaction between hydrogen and oxygen to form water is an example of a chemical reaction.


  True
• Freezing water is an example of a physical change.
• Match the reaction type with its definition:

  Synthesis ↔️ Two or more reactants combine

  Decomposition ↔️ A single reactant breaks down

  Single Displacement ↔️ One element replaces another

  Double Displacement ↔️ Two compounds exchange ions
• The balanced equation for the reaction between hydrogen and oxygen to form water is 2H₂ + O₂ → 2H₂O.


  True
• What is a chemical reaction?

  Bonds broken and rearranged
• In a physical change, what happens to the bonds between atoms?

  They are not broken
• Where are reactants listed in a chemical equation?

  Left side
• A chemical change involves changes in chemical properties and composition
• In a chemical reaction, the starting materials are called reactants and the new substances formed are called products.
• In a decomposition reaction, water breaks down into hydrogen gas and oxygen gas.


  True
• What type of reaction involves two or more reactants combining to form a single product?

  Synthesis
• What is the purpose of balancing chemical equations?

  Ensure conservation of mass
• During a chemical reaction, reactants are transformed into products
• Chemical changes are generally reversible, while physical changes are irreversible.

  False
• Reactants are listed on the left side of a chemical equation.


  True
• Steps to balance a chemical equation

  1️⃣ Identify reactants and products

  2️⃣ Count atoms of each element on both sides

  3️⃣ Adjust coefficients to balance atoms
• Chemical changes create new substances with different chemical properties
• The identity of a substance remains the same in a physical change.

  True
• Products have the same properties as reactants.

  False
• In a chemical change, bonds between atoms are broken and rearranged.

  True
• Order the common types of chemical reactions based on their definitions.

  1️⃣ Synthesis: Two or more reactants combine to form a single product

  2️⃣ Decomposition: A single reactant breaks down into two or more products

  3️⃣ Single Displacement: One element in a compound is replaced by another element

  4️⃣ Double Displacement: Two compounds exchange ions to form two new compounds
• In a single displacement reaction, sodium replaces hydrogen in HCl to form NaCl and H₂.
• In a single displacement reaction, one element replaces another in a compound.

  True
• Steps to balance a chemical equation

  1️⃣ Identify reactants and products

  2️⃣ Count atoms of each element on both sides

  3️⃣ Adjust coefficients to balance atoms
• What is a chemical reaction defined as?

  Bond rearrangement
• What happens to the composition of a substance during a physical change?

  Remains the same
• What are the starting materials in a chemical reaction called?

  Reactants
• What is the main goal of balancing chemical equations?

  Ensure conservation of mass