Energy and Chemical Processes

Energy

  • The ability to do work that can be quantified by different types of Units

    • Joule -The SI Unit of energy

    • Calorie - Unit of energy used in health professions and everyday life

Law of Conservation of Energy

  • Energy cannot be created or destroyed by any physical process

    • System - an experiment or observation

    • Surrounding - everything not a part of the system

  • energy is exchanged between the system and the surroundings

  • what happens to the system happens to the surroundings

    • If energy is lost in the system, the same amount is lost in the surroundings

Different Forms of Energy

  • Kinetic Energy - Energy in motion

  • Potential Energy - stagnant/Standing energy

  • Electrical Energy - flow of electrical charge

  • Thermal Energy - random motions of atoms and molecules in matter

  • Chemical Energy - Potential energy, Positions of the particles that compose a chemical system

Units

  • 1,000 Joules (J) =1 Kilojoule

  • 1,000 calories (Cal) = 1 kilocalorie (kcal) = 1 Calorie (Cal)

  • 1 cal = 4.184J

  • 1 Cal = 4.184 kJ

Dimensional Analysis w/ Energy Units

  • How many Joules are in 70.0 Calories

    • 4.184 J/1 cal1000cal/1 Cal70.0=293,000

Temperature

  • Measure of thermal energy of matter and can be measured using 3 Scales

  • Fahrenheit Scale

    • water freezes at 32 degrees Fahrenheit

    • water freezes at 212 degree Fahrenheit

  • Celsius Scale

    • water freezes at O degrees Celsius

    • water boils at 100 degrees Celsius

  • Kelvin Scale

    • Avoids negative temperatures by assigning o Kelvin to absolute zero, molecular motion virtually stops

Conversions

  • K = C+273.15

  • C = F- 32/1.8

  • F = (C x 1.8) + 32

  • degree symbol is only used with Celsius and Fahrenheit

Heat

  • The transfer of energy, proportional to the mass of a substance and can be measured by a change in temperature

  • If energy goes into an object, the total energy of the object increases, values of ΔT are positive

  • If energy is coming out of an object, the total energy decreases, values of heat and ΔT are negative

Energy Changes in Chemical Reactions

  • Chemical reactions are always accompanied by an energy change

    • Broken Bonds - use energy

    • Forming bonds - release energy

  • Exothermic - energy of bonds in the products is liver than the energy of the bonds in the reactants. Heat is released

  • Endothermic - energy of bonds in the products is higher than the energy of the bonds in the reactants, heat is absorbed

Heat

  • Heat = MCΔT

  • M = mass of a substance in grams

  • C = specific heat of a substance (proportionality constant)

    • J/g•°C

  • ΔT = change in temperature

    • final temp - initial temp

    • measured in Joules