Energy is the driving force behind everything in our world. From the motion of objects to the heat we feel, energy takes various forms and constantly changes. Understanding these types and transformations is key to grasping how our universe works.

Heat, temperature, and thermal energy are closely related but distinct concepts. Knowing how they differ and interact helps us make sense of everyday phenomena, from cooking to climate control. We'll also learn how to calculate heat transfer, a crucial skill in many scientific and practical applications.

Energy Types and Changes

Types and changes of energy

• Kinetic energy represents the energy of motion depends on an object's mass and velocity (moving car, flowing river)
• Potential energy is stored energy due to an object's position or configuration (stretched spring, book on a shelf)
  • Gravitational potential energy depends on an object's height and mass
  • Chemical potential energy is stored within chemical bonds
  • Elastic potential energy is stored in stretched or compressed objects
• Law of Conservation of Energy states that energy cannot be created or destroyed only converted from one form to another (energy conversion)
• Physical processes involve energy changes between kinetic and potential forms (rollercoaster converting potential to kinetic energy and vice versa)
• Chemical processes involve energy changes related to breaking and forming chemical bonds
  • Exothermic reactions release energy to the surroundings
  • Endothermic reactions absorb energy from the surroundings

Heat vs thermal energy vs temperature

• Thermal energy represents the total kinetic energy of particles in a substance due to their random motion depends on the number of particles and their average kinetic energy
• Temperature measures the average kinetic energy of particles in a substance reflects the intensity of thermal energy measured in Kelvin (K), Celsius (℃), or Fahrenheit (℉)
• Heat is the transfer of thermal energy between substances due to a temperature difference flows from higher to lower temperature measured in joules (J) or calories (cal)

Specific heat and heat capacity

• Specific heat capacity (c) is the amount of heat required to raise the temperature of 1 gram of a substance by 1 Kelvin or 1 degree Celsius measured in J/(g·K) or J/(g·℃) varies depending on the substance
• Heat capacity (C) is the amount of heat required to raise the temperature of an entire object or system by 1 Kelvin or 1 degree Celsius measured in J/K or J/℃ depends on the mass and specific heat capacity of the substance calculated using $C = mc$
• Substances with high specific heat capacities require more energy to change their temperature (water has a high specific heat capacity making it an effective coolant)
• Understanding specific heat is crucial for heat transfer applications (cooking, insulation, climate control systems)

Calculations for heat transfer

• Heat transfer can be calculated using the formula $Q = mc\Delta T$ where Q is heat transferred (J), m is mass (g), c is specific heat capacity (J/(g·K) or J/(g·℃)), and $\Delta T$ is temperature change (K or ℃)
• Steps to calculate heat transfer:
  1. Identify the mass, specific heat capacity, and temperature change of the substance
  2. Substitute the values into the heat transfer formula
  3. Solve for Q to determine the amount of heat transferred
• Example: Calculate the heat required to raise the temperature of 500 g of water from 20℃ to 80℃ (specific heat capacity of water: 4.18 J/(g·℃))
  • $Q = mc\Delta T$
  • $Q = (500\text{ g})(4.18\text{ J/(g·℃)})(80℃ - 20℃)$
  • $Q = (500\text{ g})(4.18\text{ J/(g·℃)})(60℃)$
  • $Q = 125,400\text{ J}$ or 125.4 kJ

Energy, Work, and Power

• Work is the transfer of energy when a force is applied to an object, causing it to move in the direction of the force
• Force is any interaction that, when unopposed, will change the motion of an object
• Power is the rate at which work is done or energy is transferred, measured in watts (joules per second)
• Thermodynamics is the study of heat and temperature and their relation to energy and work
• Entropy is a measure of the disorder or randomness in a system, which tends to increase in natural processes