Chapter 6 - Thermochemistry

6.1 - The Nature of Energy and Types of Energy

• Energy is a commonly used phrase that refers to an abstract idea.
  • The capacity to conduct labor is how most people describe energy.
  • Work is defined by chemists as the directed energy change that occurs as a result of a process.
  • The sun's radiant energy, often known as solar energy, is the Earth's major source of energy.
  • Solar energy heats the atmosphere and the surface of the Earth encourages plant development through the process of photosynthesis and influences global climate patterns.
  • The energy associated with the random motion of atoms and molecules is known as thermal energy.
  • The structural units of chemical compounds store chemical energy.
  • The energy accessible as a result of an object's position is known as potential energy.

6.2 - Energy Changes in Chemical Reactions

• It's crucial to know the difference between thermal energy and heat.
  • The study of heat change in chemical reactions is known as thermochemistry.
  • To investigate energy changes caused by chemical processes, we must first define the system or the region of the universe that we are interested in.
  • Outside the system, the environs are the rest of the cosmos.
  • An open system can exchange mass and energy with its surroundings, mainly in the form of heat.
  • A closed system that permits energy (heat) but not masses to be transferred.
  • We can create an isolated system by enclosing the water in a completely insulated container that prevents the transfer of mass or energy.
• This reaction is an exothermic process, which is defined as any process that emits heat or transfers thermal energy to the environment.

6.3 - Introduction to Thermodynamics

• Thermochemistry is a subset of the larger field of thermodynamics.
  • The scientific study of the interconversion of heat and other types of energy is known as thermodynamics.
• Thermodynamics is the study of changes in a system's state
  • Which is characterized by all-important macroscopic parameters such as composition, energy, temperature, pressure, and volume.
• State functions are attributes that are determined by the state of the system, independent of how that condition was attained.
  • Energy, pressure, volume, and temperature are examples of state functions.
• Energy can be changed from one form to another, but it cannot be created or destroyed,
  • According to the first law of thermodynamics, which is based on the law of conservation of energy.

6.4 - Enthalpy of Chemical Reactions

• The difference in the enthalpies of the products is defined as the change in enthalpy, also known as the enthalpy of reaction, Hrxn.
  • The term "per mole" in the unit for H refers to the enthalpy change per mole of the reaction as written—that is, when one mole of ice is changed to one mole of liquid water.
• Thermochemical equations, which depict enthalpy changes and mass interactions.

6.5 - Calorimetry

• A calorimeter, a closed container created expressly for this purpose, is used in the laboratory to detect heat changes in physical and chemical processes.
  • Understanding of specific heat and heat capacity is required for calorimetry, the measurement of heat changes.
• The amount of heat required to raise the temperature of one gram of a substance by one degree Celsius is known as its specific heat (s). It is measured in J/g °C.
  • The amount of heat required to raise the temperature of a given quantity of a substance by one degree Celsius is called the heat capacity (C) of the substance.

6.6 - Standard Enthalpy of Formation and Reaction

• The standard enthalpy of formation (Hf °) is the "sea level" reference point for all enthalpy formulations.
  • At 1 atm, a substance is said to be in its standard state, hence the phrase "standard enthalpy."
• The change in enthalpy when reactants are transformed into products is the same whether the reaction takes place in one step or a series of steps, according to Hess's law.

6.7 - Heat of Solution and Dilution

• When a specific amount of solute dissolves in a certain amount of solvent, the heat of solution, or enthalpy of solution, Hsoln, is created or absorbed.
• The heat of hydration, or Hhydr, is the enthalpy change associated with the hydration process.
• The heat of dilution refers to the temperature change that occurs during the dilution process.