Balancing Equations and Reactions

Balancing Equations and Conservation of Mass

• The Law of Conservation of Mass states matter is neither created nor destroyed during a chemical reaction.
• The number of atoms in each element remains constant before and after a reaction.
• The total mass of the reactants equals the total mass of the products.
• Chemical equations are balanced to adhere to the Law of Conservation of Mass.

Classifying and Identifying Reactions

• The 5 types of chemical reactions are synthesis, decomposition, single displacement, double displacement, and combustion.

Synthesis Reaction

• Two or more reactants combine to form a single, larger, more complex product.
• Formula: A + B → AB
• Example: 2H₂ + O₂ → 2H₂O

Decomposition Reaction

• A complex molecule breaks down into simpler products.
• Formula: AB → A + B
• Example: 2H₂O → 2H₂ + O₂

Single Displacement Reaction

• One element displaces another in a compound, creating a new compound and a new single element.
• Formula: A + BC → AC + B
• Example: Zn + H₂S → H₂ + ZnS, where zinc displaces hydrogen.

Double Displacement Reaction

• Elements exchange places, resulting in two new compounds.
• Formula: AD + BC → AC + BD
• Example: AgNO₃ + NaCl → AgCl + NaNO₃, where Ag and Na switch places.

Combustion Reaction

• A reaction between a fuel (like methane) and oxygen, producing carbon dioxide and water.
• Formula: Fuel + O₂ → H₂O + CO₂
• Example: CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)

Factors Affecting Rate of Reaction

• Collision Theory: The greater the frequency of collisions between reactant particles, the greater the rate of reaction.
• The components of the collision theory are: Activation Energy, Frequency of Collisions and Orientation of a Collision

Activation Energy

• Particles require a minimum amount of energy to react.
• If particles collide with less energy than this barrier, they bounce off and no reaction occurs.

Frequency of Collisions

• The number of collisions between reactant particles.
• More collisions raise the probability of a reaction.

Orientation of a Collision

• Particles must collide in a specific orientation for the correct atoms to contact each other and cause a reaction.

Factors affecting reaction rate

• Temperature: Directly proportional to the reaction rate; higher temperature means faster-moving particles and more frequent collisions.
• Concentration of Reactants: Higher concentration leads to more reactant particles, more collisions, and a faster reaction rate.
• Increased Surface Area of Solid Reactants: More surface area results in more reactant molecule collisions, increasing the reaction rate.
• Catalysts: Substances that lower the activation energy, thus altering the reaction rate.
  • Catalysts are not consumed in the reaction and do not change the products.
  • Catalysts can provide a reaction surface.
  • Catalysts ensure reactant molecules are favorably angled for collision, increasing success.
  • Catalysts are subjective in nature.

Properties of Ionic Compounds

• Ionic compounds are solid, giant, crystalline structures made of ions held together by strong electrostatic attraction.
• High melting and boiling points due to strong electrostatic forces.
• Solid ionic compounds do not conduct electricity because ions need much energy to break electrostatic forces and ionic bonds.
• When dissolved in water, ionic compounds disassemble into free-moving ions, enabling electrical conductivity.

Physical Properties of Matter

• Volume and Shape
• Density
• Compressibility
• Thermal Expansion (change in volume due to temperature change)

Phase Transitions

• Endothermic Reaction: Energy is absorbed, providing activation energy. Examples: melting, sublimation, and evaporation.
• Exothermic Reaction: Heat energy is released. Examples: freezing, condensation, and deposition.

Kinetic Molecular Theory (KMT)

• Five statements explaining the physical behavior of solids, liquids, and gases.
  • Matter is made of tiny particles with definite, unchangeable sizes.
  • The particles are in constant, random motion, possessing kinetic energy.
  • The particles interact through attractions and repulsions, possessing potential energy.
  • The kinetic energy (velocity) of the particles increases as temperature increases, a directly proportional relationship.
  • Particles in a system transfer energy via elastic collisions. If they have the required orientation and activation energy, new bonds and products form.

Acids and Bases

• Acid: A substance in water with a sour taste and a pH less than 7.
• Base: A substance in water with a bitter taste, slippery feel, and a pH greater than 7.

Arrhenius Theory

• Arrhenius Acid: Any species that increases the concentration of H+ (hydrogen ions) in an aqueous solution.
  • Example: NaOH(aq)
• Arrhenius Base: Any species that increases the concentration of OH- (hydroxide ions) in an aqueous solution.
  • Example: NaOH(aq) → Na+(aq) + OH-(aq)
• Limitations: Only applies to acid-base chemistry in aqueous solutions.

Bronsted-Lowry Acid-Base Theory

• When an acid and base react, the acid forms its conjugate base, and the base forms its conjugate acid by exchanging a proton (H+).
• Bronsted-Lowry Acid: A substance that donates a proton (H+ ion), i.e., a proton donor.
• Bronsted-Lowry Base: A substance that accepts a proton (H+ ion), i.e., a proton acceptor.

Conjugate Acid-Base Pairs

• Conjugate means joined together as a pair.
• Every BL base has a conjugate acid, and every BL acid has a conjugate base.
• A conjugate acid-base pair consists of two species (one an acid and one a base) differing by the loss or gain of a proton.
• Formula: HA + B = HB+ + A

Common Strong Acids/Bases

• Acids: Hydrochloric Acid (HCl), Nitric Acid (HNO₃)
• Bases: Lithium Hydroxide (LiOH), Sodium Hydroxide (NaOH)

Neutralization Reaction

• A chemical reaction between an acid and a hydroxide base produces salt and water.
• Word equation: acid + base → salt + water
• It is a double displacement reaction.
• Potassium Hydroxide + Hydrochloric Acid → Potassium Chloride + Water
• Magnesium Oxide + Sulphuric Acid → Magnesium Sulphate + Water
• Copper Oxide + Nitric Acid → Copper Nitrate + Water
• Calcium Oxide + Hydrochloric Acid → Calcium Chloride + Water

Molarity

• How do we calculate molar mass?