ENERGY

1
ENERGY

• The capacity to do work or produce heat.

2
Law of conservation of energy

• In any chemical process energy can be converted
  from one form to another, but cannot be created
  or destroyed.

3
Potential Energy

• .Energy due to position or composition.
• A boulder at the top of a cliff
• Gasoline

4
Kinetic Energy

• Energy due to the motion of an object
• Depends on the mass and the velocity of the
  object.
• KE1/2 mv2

5
Frictional heating

• The transfer of energy due to contact between
  surfaces

6
Work

• Involves a transfer of energy.
• Defined as force acting over distance.
• Depends on pathway.

7
State function or property

• Depends only on its present state. Does not
  depend on how the system arrived at the present
  state. Energy is a state function.

8
Internal energy E

• The sum of the kinetic and potential energies of
  all the particles in a system.
• Can be changed by a flow of heat or work.

9
Temperature

• A property that reflects the random motion of
  particles in a substance.
• The average kinetic energy of the system.

10
Heat (q)

• The transfer of energy between two objects
  because of a temperature difference.

11
Units of Heat

• calorie-the amount of heat needed to raise the
  temp. of 1g of water 1C
• Calorie 1000 calories
• Joule (J) SI unit of energy 4.184J 1cal

12
Thermochemical reactions

• System - the part of the universe where the
  reaction is taking place.
• Surroundings - the rest of the universe.

13
Thermochemical reactions

• Exothermic - energy is flowing out of the system
  into the surroundings.
• Endothermic - energy is flowing into the system
  out of the surroundings.

14
Calorimetry

• The science of measuring heat based on
  temperature change when a body absorbs or gives
  off heat.

15
Heat capacity (J/C)

• The amount of heat energy needed to increase the
  temperature of an object 1C.

16
Specific Heat Capacity(J/gC)

• Specific heat (S)
• Amount of heat energy needed to raise the
  temperature of 1g of a substance 1C

17
Enthalpy(H)

• The heat content of a system at constant
  pressure.
• D Hq

18
Constant Pressure Calorimetry

• Atmospheric pressure is maintained during the
  process.
• Styrofoam cup calorimeter.

19
Constant Volume Calorimetry

• Process is carried out in a sealed container
  (bomb calorimeter). Volume does not change,
  pressure does.

20

• 1.00 mole of steam condenses to water at 1 atm
  and 100oC. The steam occupied 30.6L and the
  liquid has a density of 0.996 g/mL. If 40.66 kJ
  of heat is released what is the DE for this
  condensation?

21
H2 O2? H2O DH-572kJ

• How much heat is released in the formation of 1
  mol of water?
• How much heat is released when 4.03g of H2
  completely reacts?
• How much heat is released when 186 g of O2
  reacts completely?

22
The specific heat of silver 0.24 J/goC

• How much energy is required to raise the temp. of
  150.g Ag from 273K to 298K?
• What is the molar heat capacity of silver?

23

• 5.00g of Al pellets and 10.0g of Fe pellets are
  heated to 100.0OC. The pellets are then dropped
  into 97.3 g of water at 22.0oC. What is the final
  temp of the water and the metals assuming no heat
  is lost to the surroundings?

24

• A 0.1964 g sample of quinone C6H4O2 is burned in
  a bomb calorimeter with a heat capacity of 1.56
  kJ/oC.The temp of the calorimeter increases by
  3.2oC. What is the energy of combustion of
  quinone per mol?

25
HESSS LAW

• In a chemical change, the change in enthalpy is
  the same whether the reaction takes place in one
  step or in several steps.

26
Hesss Law

• If you add 2 or more thermochemical equations to
  give a final equation, you can also add the heats
  of reaction to give a total heat of reaction.

27
Rules for heat change

• If the reaction is reversed the sign on enthalpy
  is also reversed.
• If the reaction is multiplied by a number the
  enthalpy must be multiplied by the same number.

28
Standard heat of formation ?Hf

• The change in enthalpy that occurs when one mole
  of a compound is formed from its elements. All
  substances are in their standard state.

29
Standard States

• The state the element or compound exists in at 1
  atm and 25C.
• ?Hf of an element is 0.

30
Standard States for Compounds

• Gaseous substance the pressure is 1 atm.
• Solution the concentration is 1 M.
• Pure substance in condensed state.