Chemical Equations Quiz

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Questions and Answers

What does the symbol (aq) represent in a chemical equation?

  • Aqueous, meaning dissolved in water (correct)
  • Acidic, indicating the presence of an acid
  • Atmospheric, indicating gas in the air
  • Alkaline, indicating a base solution

What is the first step in writing a chemical equation?

  • Creating a word equation (correct)
  • Writing the balanced equation
  • Formulating the skeleton equation
  • Identifying reactants and products

Which of the following represents a skeleton equation?

  • H2O is produced from H2 and O2
  • H2 + O2 → H2O (correct)
  • Water is formed by hydrogen and oxygen
  • 2H2 + O2 → 2H2O

What is the importance of balancing chemical equations?

<p>It helps predict the formation of products (D)</p> Signup and view all the answers

In the example of propane combustion, how many water molecules are produced?

<p>4 H2O (B)</p> Signup and view all the answers

How many oxygen molecules are needed for the complete combustion of one propane molecule?

<p>5 O2 (B)</p> Signup and view all the answers

What does balancing a chemical equation ensure?

<p>The law of conservation of mass is obeyed (D)</p> Signup and view all the answers

Which element had to be balanced first in the propane combustion example?

<p>Carbon (C)</p> Signup and view all the answers

What must be adjusted to balance the oxygen in the propane combustion reaction?

<p>Coefficient of O2 (B)</p> Signup and view all the answers

In a balanced chemical equation, what must remain equal on both sides?

<p>Number of atoms of each element (B)</p> Signup and view all the answers

What are the substances called that undergo change during a chemical reaction?

<p>Reactants (B)</p> Signup and view all the answers

What does the arrow (→) in a chemical equation indicate?

<p>The direction of the reaction (C)</p> Signup and view all the answers

In the equation 2H₂ + O₂ → 2H₂O, what does the coefficient '2' in front of H₂ and H₂O represent?

<p>Number of molecules (C)</p> Signup and view all the answers

What law dictates that the mass of reactants must equal the mass of products in a chemical reaction?

<p>Law of conservation of mass (C)</p> Signup and view all the answers

What are small numbers written at the lower right of a chemical symbol called?

<p>Subscripts (D)</p> Signup and view all the answers

Which of the following statements about chemical equations is FALSE?

<p>An arrow indicates the mass of the reactants. (A)</p> Signup and view all the answers

In reversible reactions, how is the arrow represented in the chemical equation?

<p>⇌ (B)</p> Signup and view all the answers

What do the physical states in chemical equations help to indicate?

<p>The state of matter of reactants and products (C)</p> Signup and view all the answers

What does the subscript '2' in Hâ‚‚O indicate?

<p>Two hydrogen atoms in a water molecule (C)</p> Signup and view all the answers

Which of the following is NOT a component of a chemical equation?

<p>Catalysts (B)</p> Signup and view all the answers

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Study Notes

Chemical Equations

  • Definition: Symbolic representations of chemical reactions where reactants transform into products.
  • Law of Conservation of Mass: States that matter can't be created or destroyed in a reaction, meaning the mass of reactants equals the mass of products.
  • Reactants: Substances at the start of a reaction that undergo change.
  • Products: New substances formed as a result of a reaction.
  • Arrow (→): Separates reactants from products, indicating reaction direction.
  • Coefficients: Numbers in front of chemical formulas indicating the number of molecules or moles of each substance.
  • Subscripts: Small numbers at the lower right of a chemical symbol, indicating the number of atoms of each element in a molecule.
  • States of Matter: Indicate the physical state of reactants and products:
    • (s) solid
    • (l) liquid
    • (g) gas
    • (aq) aqueous (dissolved in water)

Writing Chemical Equations

  • Word Equations: Describe the reaction in words, helping to identify reactants and products.
  • Skeleton Equations: Use chemical formulas instead of words, but are not yet balanced.
  • Balancing Chemical Equations: Adds coefficients to chemical formulas to ensure equal numbers of each element on both sides of the equation, upholding the law of conservation of mass.

Balancing Example: Combustion of Propane

  • Reaction: Propane (C₃H₈) burns with oxygen (Oâ‚‚) to produce carbon dioxide (COâ‚‚) and water (Hâ‚‚O).
  • Skeleton Equation: C₃H₈ + Oâ‚‚ → COâ‚‚ + Hâ‚‚O
  • Balancing Steps:
    1. Count atoms of each element on both sides of the equation.
    2. Balance carbon atoms by adding a coefficient of 3 in front of COâ‚‚.
    3. Balance hydrogen atoms by adding a coefficient of 4 in front of Hâ‚‚O.
    4. Balance oxygen atoms by adjusting the coefficient of Oâ‚‚ to 5.
  • Balanced Equation: C₃H₈ + 5Oâ‚‚ → 3COâ‚‚ + 4Hâ‚‚O

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