Chemical Reactions: Basics and Types

• Chemical reactions involve the rearrangement of atoms and molecules to form new substances

Basics of Chemical Reactions

• Reactants are the starting materials in a chemical reaction
• Products are the substances formed as a result of a chemical reaction
• Chemical equations represent chemical reactions using chemical formulas and symbols
• Balancing chemical equations ensures that the number of atoms of each element is the same on both sides of the equation, adhering to the law of conservation of mass

Types of Chemical Reactions

• Synthesis (or combination) reactions occur when two or more reactants combine to form a single product (A + B → AB)
• Decomposition reactions involve a single reactant breaking down into two or more products (AB → A + B)
• Single displacement (or single replacement) reactions occur when one element replaces another in a compound (A + BC → AC + B)
• Double displacement (or double replacement) reactions involve the exchange of ions between two compounds to form two new compounds (AB + CD → AD + CB)
• Combustion reactions involve the rapid reaction between a substance with an oxidant, usually oxygen, to produce heat and light
• Acid-base reactions involve the transfer of protons (H+) between reactants, forming salt and water

Balancing Chemical Equations

• Write the unbalanced equation with correct chemical formulas for each reactant and product
• Count the number of atoms of each element on both sides of the equation
• Adjust coefficients (the numbers in front of the chemical formulas) to balance the number of atoms of each element
• Start with elements that appear in only one reactant and one product
• Balance polyatomic ions as a single unit if they appear unchanged on both sides of the equation
• Verify that the equation is balanced by recounting the number of atoms of each element on both sides

Energy Changes in Chemical Reactions

• Exothermic reactions release energy in the form of heat (ΔH < 0)
• Endothermic reactions absorb energy from their surroundings (ΔH > 0)
• Activation energy is the minimum energy required for a chemical reaction to occur
• Catalysts speed up chemical reactions by lowering the activation energy without being consumed in the reaction

Reaction Rates

• Reaction rate is the speed at which a chemical reaction occurs
• Factors affecting reaction rates:
  • Concentration of reactants: Higher concentration usually increases the reaction rate
  • Temperature: Higher temperature usually increases the reaction rate
  • Surface area: Increased surface area of solid reactants increases the reaction rate
  • Catalysts: Catalysts increase reaction rates

Oxidation-Reduction (Redox) Reactions

• Oxidation is the loss of electrons, resulting in an increase in oxidation number
• Reduction is the gain of electrons, resulting in a decrease in oxidation number
• Oxidizing agents accept electrons and cause oxidation
• Reducing agents donate electrons and cause reduction
• Redox reactions always occur together; one substance is oxidized while another is reduced

Acids and Bases

• Acids are substances that donate protons (H+) or accept electrons; they have a pH less than 7
• Bases are substances that accept protons (H+) or donate electrons; they have a pH greater than 7
• Neutralization is the reaction between an acid and a base, forming salt and water
• pH is a measure of the acidity or basicity of a solution
• Acid-base indicators are substances that change color depending on the pH of the solution

Chemical Equilibrium

• Chemical equilibrium is the state in which the rate of the forward reaction equals the rate of the reverse reaction
• At equilibrium, the concentrations of reactants and products remain constant
• Le Chatelier's principle states that if a change of condition (e.g., temperature, pressure, concentration) is applied to a system in equilibrium, the system will shift in a direction that relieves the stress
• Equilibrium constant (K) is the ratio of product concentrations to reactant concentrations at equilibrium

Stoichiometry

• Stoichiometry is the quantitative relationship between reactants and products in a chemical reaction
• Mole ratio is the ratio of the number of moles of reactants and products in a balanced chemical equation
• Limiting reactant is the reactant that is completely consumed in a reaction and determines the amount of product formed
• Excess reactant is the reactant that is present in more than the amount required to react with the limiting reactant
• Theoretical yield is the maximum amount of product that can be formed from a given amount of reactants
• Actual yield is the amount of product actually obtained from a reaction
• Percent yield is the ratio of the actual yield to the theoretical yield, expressed as a percentage

Solutions

• A solution is a homogeneous mixture of two or more substances
• Solute is the substance being dissolved
• Solvent is the substance doing the dissolving
• Concentration is the amount of solute present in a given amount of solvent or solution
• Molarity (M) is the number of moles of solute per liter of solution
• Solubility is the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature
• Factors affecting solubility include temperature and pressure

Explore the basics of chemical reactions, including reactants, products, and balancing equations. Learn about synthesis, decomposition, single displacement, and double displacement reactions with examples. Understand how these reactions transform substances and conserve mass.