topic 4

• What is enthalpy?


  Enthalpy is the stored chemical potential energy resulting from the attractive and repulsive forces between charged particles.
• What does the difference in enthalpy represent?

  The difference in enthalpy represents the heat energy released or absorbed during a chemical reaction.
• What is a system in the context of a chemical reaction?

  A system is a collection of particles involved in a chemical reaction.
• What are the surroundings in a chemical reaction?

  The surroundings are everything outside of the chemical reaction.
• How is the change in enthalpy calculated?


  The change in enthalpy is calculated as \( \Delta H = H_{\text{products}} - H_{\text{reactants}} \).
• What are the characteristics of exothermic reactions?

  • Enthalpy of reactants is greater than that of products.
  • Change in enthalpy is negative.
  • More energy is released to form bonds than absorbed to break bonds.
  • Enthalpy is converted into heat energy released to the surroundings, increasing temperature.
  • Examples: combustion, respiration, condensation, solidification.
• What are the characteristics of endothermic reactions?

  • Enthalpy of reactants is less than that of products.
  • Change in enthalpy is positive.
  • More energy is absorbed to break bonds than released to form bonds.
  • Heat energy from the surroundings is absorbed by the system, decreasing temperature.
  • Examples: photosynthesis, melting, vaporization, sublimation.
• What happens to energy when bonds are broken and formed?

  Energy is required to break bonds, increasing the stored potential energy, while energy is released when bonds are formed.
• What is the activation energy in a chemical reaction?

  The activation energy is the minimum energy required for the reaction to occur and to reach the transition state.
• How do catalysts affect activation energy?

  Catalysts provide an alternative reaction pathway with a lower activation energy.
• What is the Collision Theory in chemical reactions?

  • Reactant particles must collide to react.
  • Collisions must have sufficient energy (activation energy).
  • Correct orientation of particles is necessary for a successful collision.
• What happens to the rate of reaction as the activation energy increases?

  The greater the activation energy, the slower the reaction.
• What is the transition state in a chemical reaction?

  The transition state is the highest energy intermediate state during the reaction.
• What factors affect the rate of chemical reactions?

  1. Nature of Reactants: Strong bonds lead to slower reactions.
  2. Concentration: Higher concentration increases collision frequency.
  3. Surface Area: Greater surface area increases collision frequency.
  4. Temperature: Higher temperature increases kinetic energy and collision frequency.
  5. Catalysts: Lower activation energy increases successful collisions.
• How does increasing the concentration affect the reaction rate?

  Increasing concentration increases number of reactant particles in same volume. Increases the frequency of collisions, leading to a higher reaction rate.
• How does increasing the surface area of reactants affect the reaction rate?

  Increasing surface area exposes more reactant particles to collisions, increasing the reaction rate.
• How does increasing temperature affect the reaction rate?

  Increasing temperature increases the average kinetic energy of particles, which means particles are moving faster. This increases the frequency of collisions. Greater proportion of reactant particles possess the minimum required activation energy to collide, proportion of successful collisions increases
• What is the relationship between catalysts and reaction rates?

  Catalysts increase the reaction rate by providing an alternative pathway with lower activation energy.
• What are the key points of the General Kinetic Theory of gases?

  • All matter is made up of particles.
  • Particles are in constant motion.
  • Increase in temperature increases average kinetic energy.
  • States of matter differ in strength of forces and freedom of movement.
• What happens to gases at lower temperatures according to the Real Gases concept?

  Forces of attraction and repulsion become significant, and gases may liquefy to form solids at low temperatures.
• What is temperature in the context of gases?

  Temperature is the average kinetic energy of particles of a substance.
• What is heat in the context of gases?

  Heat is the energy transferred between objects at different temperatures.
• How does mass affect the velocity of gas particles?

  Greater mass results in lower velocity of particles, while lower mass results in greater velocity.
• What are the key points of the Kinetic Theory of Gases?

  • Gases consist of molecules.
  • Molecules exhibit rapid, random, straight-line motion.
  • Gas particles are large distances apart; their size is negligible.
  • Average kinetic energy is directly proportional to temperature.
  • Particles exert negligible forces of attraction or repulsion.
  • Collisions are perfectly elastic.
• What causes gas pressure?

  Gas pressure is caused by collisions of particles with the walls of the container and with each other.
• What factors determine gas pressure?

  Gas pressure depends on the frequency and force of collisions in a given area.
• What are Boyle's Law, Charles' Law, and the relationship between pressure and temperature in gases?

  • Boyle's Law: At constant temperature, volume is inversely proportional to pressure.
  • Charles' Law: At constant pressure, volume is directly proportional to absolute temperature.
  • Pressure and Temperature: At constant volume, pressure is directly proportional to temperature.
• What does Boyle's Law state about the relationship between volume and pressure?

  Boyle's Law states that at constant temperature, the volume of a gas is inversely proportional to its pressure.
• What does Charles' Law state about the relationship between volume and temperature?

  Charles' Law states that at constant pressure, the volume of a gas is directly proportional to its absolute temperature.
• What happens to pressure when a gas in a fixed volume is heated?

  When heated, the kinetic energy increases, leading to greater velocity and more frequent collisions, increasing pressure.
• What is Avogadro's law regarding gases?

  • Equal volumes of all gases at the same temperature and pressure contain equal numbers of particles (moles).
• What is a limiting reagent in a chemical reaction?

  • The limiting reagent is the reactant that is completely used up, determining the amount of product formed.
  • The excess reagent is the reactant that is not completely used up.