Chemical Equations from word descriptions(skeleton equations and word equations)

Introduction to Writing Chemical Equations

• Convert word descriptions of reactions into balanced chemical equations.

Diatomic Molecules

• Diatomic Elements: Fluorine (F₂), Nitrogen (N₂), Oxygen (O₂), Chlorine (Cl₂), Bromine (Br₂), Iodine (I₂), Hydrogen (H₂).

• Importance of recognizing these molecules when writing equations.

Example 1: Phosphorus and Fluorine Reaction

• Reactants: Solid elemental phosphorus (P₄) reacts with fluorine gas (F₂).

• Product: Phosphorus pentafluoride (PF₅), which is a gas.

Balancing the Equation

• Initial phosphorus: 4 (from P₄); Initial fluorine: 2 (from F₂)

• Balancing Phosphorus:

  • Place a coefficient of 4 in front of PF₅ ➔ 4 P and 20 F.

• Balancing Fluorine:

  • Need to equal 20 F ➔ Place a coefficient of 10 in front of F₂.

• Balanced Equation: 4 P₄ + 10 F₂ ➔ 4 PF₅.

Example 2: Calcium and Nitrogen Reaction

• Reactants: Calcium metal (Ca) and nitrogen gas (N₂).

• Product: Calcium nitride (Ca₃N₂).

Writing the Formula for Calcium Nitride

• Calcium has a +2 charge; Nitride has a -3 charge.

• Need three calcium ions and two nitride ions for charge balance.

Balancing the Equation

• Calcium atoms: 1 (left) vs. 3 (right).

• Balancing Calcium: Place a coefficient of 3 in front of Ca on the left.

• Balanced Equation: 3 Ca + N₂ ➔ Ca₃N₂.

Example 3: Sulfur and Oxygen Reaction

• Reactants: Solid sulfur (S₈) and oxygen gas (O₂).

• Product: Sulfur trioxide (SO₃).

Balancing the Equation

• Sulfur atoms: 8 (S₈) vs. 1 (SO₃).

• Balancing Sulfur: Place a coefficient of 8 in front of SO₃.

• Total oxygen now becomes 24 on the right ➔ Need 12 O₂ on the left.

• Balanced Equation: S₈ + 12 O₂ ➔ 8 SO₃.

Example 4: Hydrochloric Acid Reaction

• Reactants: Hydrochloric acid (HCl) and barium hydroxide (Ba(OH)₂).

• Products: Water (H₂O) and barium chloride (BaCl₂).

Writing the Chemical Formulas

• HCl is aqueous; Ba(OH)₂ is aqueous as well.

• Ba has a +2 charge; OH has a -1 charge ➔ Ba(OH)₂.

• Barium chloride formula: BaCl₂ (also aqueous).

Balancing the Equation

• Hydrogen atoms: 3 on left (1 from HCl and 2 from Ba(OH)₂) vs. 2 on right.

• Balancing requires putting a coefficient of 2 in front of HCl and 2 in front of H₂O.

• Balanced Equation: 2 HCl + Ba(OH)₂ ➔ BaCl₂ + 2 H₂O.

Example 5: Zinc and Hydrobromic Acid Reaction

• Reactants: Zinc solid (Zn) and hydrobromic acid (HBr).

• Products: Hydrogen gas (H₂) and zinc bromide (ZnBr₂).

Determining the Type of Reaction

• This is a single replacement reaction where Zn replaces H in HBr.

Balancing the Equation

• Initially, we have Zn: 1, H: 2 on right, Br: 2 on right.

• Balancing Bromine: Place a coefficient of 2 in front of HBr.

• Balanced Equation: Zn + 2 HBr ➔ H₂ + ZnBr₂.

Example 6: Combustion of Pentane

• Reactants: Pentane (C₅H₁₂, liquid) reacts with oxygen gas (O₂).

• Products: Water (H₂O, liquid) and carbon dioxide (CO₂, gas).

Steps to Balance a Combustion Reaction

• Balance carbon atoms first, then hydrogen, and lastly oxygen.

• For C₅H₁₂, need 5 CO₂ for carbon balance and 6 H₂O for hydrogen.

• Total oxygen on right side becomes 16, thus place a coefficient of 8 in front of O₂.

• Balanced Equation: C₅H₁₂ + 8 O₂ ➔ 5 CO₂ + 6 H₂O.

Diatomic Molecules

• Diatomic Elements: These are molecules composed of two atoms. The key diatomic molecules include:

  • Fluorine (F₂)

  • Nitrogen (N₂)

  • Oxygen (O₂)

  • Chlorine (Cl₂)

  • Bromine (Br₂)

  • Iodine (I₂)

  • Hydrogen (H₂)

• Importance: Recognizing these diatomic molecules is essential when writing chemical equations as they exist in pairs in their elemental forms.

• Have no fear of ice cold beer(Hydrogen, Nitrogen, Fluorine, Oxygen, Chlorine, Bromine)