Energy 2007a
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ENERGY
Potential Energy
Energy of position
Kinetic Energy
Energy of motion KE=1/2 mv2 All atoms are in motion, therefore all have KE. [except at absolute zero…0K …– 273C]
Law of Conservation of Energy
State: “Energy can be converted from one form to another, but can neither be created nor destroyed”
WORK “Force over a distance” F=ma [force = mass x acceleration] . . .Newton's 2nd law meter kg m 2 Newtons = kilograms x N kg m sec sec 2 sec 2 kg m 2 Work force x distance = Joules [also N-m] 2 sec Work kg m 2 Power = watts 3 time sec
State Function
“state function is a PROPERTY of the system that changes INDEPENDENTLY of its pathway”. ENERGY is a state function! The energy in a system is NOT dependent on the path the system took to reach that state.
Example of State function The energy difference of a boulder between the top of a mountain and the bottom is fixed. It does not matter if a boulder rolls down the side or is carried down by a helicopter, the potential energy difference possessed by the boulder is the same regardless of the path down the mountain.
Other State Functions
Density is a state function
Temperature is a state function
density does not depend on how much matter you have.
The temperature of a piece of aluminum is independent of the amount of aluminum.
Pressure is independent of the of the container size.
NOT State Functions “dependent”
Heat and work are not state functions
The more mass you have, the more heat you have The more mass you have the more work can be done.
Temperature vs. Heat
Temperature is “Average heat” Heat is a measure of molecules in motion.
Heat may be defined as:
“the flow of energy due to a temperature difference”
The flow of energy called heat is the way in which “thermal energy” is transferred from a hot object to a colder object.
System vs. Surrounding
Exothermic = negative change in energy Endothermic = positive change in energy
EXOTHERMIC
ENDOTHERMIC
Measuring Energy Change
calorie (lower case –c-) is defined as the amount of energy (heat) required to raise the temperature of one gram of water by one degree Celsius. One Calorie (capital –C- ) is one kilocalorie …. 1000 calories. The SI unit for heat is the Joule (J). 1 cal = 4.18 Joules
Conversion from Joule to calories and calories to Joules
How many calories is 700 Joules? calorie calories 700.0J x 167.5 calories 4.18J
How many Joules is 3400.0 calories? 4.18J Joules = 3400.0 calories x 813.4 Joules cal
Specific Heat Capacity
“The amount of heat required to change the temperature of one gram of a substance by one degree Celsius.
1 cal cal The Specific heat of water is 1.000 o 1g x 1 C g Co 1 cal 4.18 J 1 cal 4.18 J i.e. or or or o o g C g C g T g T
Sp Heat of other substances units = J/g-C
Water . . . . . 4.18 Aluminum . . 0.89 Iron . . . . . . 0..45 Gold . . . . . . . 0.13 How much heat is required to raise the temperature 100.0 g of each of these from 25C to 100C?
ENERGY(kiloJoules) = s x m ΔT ΔT = 75C grams = m = 100.0g
Water: kJ= 4.18J x 100 x 75 = 31,350J (31.4kJ) Aluminum: kJ = 0.89 x 100 x 75 =6675J (6.7kJ) Iron: kJ = 0.45 x 100 x 75 = 3375J (3.4kJ) Gold: kJ = 0.13 x 100 x 75 = 975J (0.975kJ)
Laws of Thermodynamics (3) 1st Law of Thermodynamics states: “ The energy of the universe is constant” 2nd Law of Thermodynamics states: “The universe is proceeding from order to disorder . . .entropy (S) is increasing” 3rd Law of Thermodynamics states: “The entropy (S) of a perfect crystal at absolute zero is zero . . .
ENTHALPY
Enthalpy is an energy function Enthalpy is a measure of heat produced or absorbed in a chemical reaction. At constant pressure enthalpy is: ∆ Hp ∆Hp = heat
Calculation
When one mole of methane is combusted, the measured heat is 890kJ; How much heat is produced by burning 11.8 g CH4?
mol CH 4 -890kJ Joules 11.8g CH 4 x x = -654.6kJ 16.042 g CH 4 mol CH 4
Why minus?
Hess’s Law
“… in going from a particular set of reactants to a particular set of products, the change in enthalpy (heat) ∆H is the SAME whether the reactions takes place in one step or a series of steps.
Potential Energy
Energy of position
Kinetic Energy
Energy of motion KE=1/2 mv2 All atoms are in motion, therefore all have KE. [except at absolute zero…0K …– 273C]
Law of Conservation of Energy
State: “Energy can be converted from one form to another, but can neither be created nor destroyed”
WORK “Force over a distance” F=ma [force = mass x acceleration] . . .Newton's 2nd law meter kg m 2 Newtons = kilograms x N kg m sec sec 2 sec 2 kg m 2 Work force x distance = Joules [also N-m] 2 sec Work kg m 2 Power = watts 3 time sec
State Function
“state function is a PROPERTY of the system that changes INDEPENDENTLY of its pathway”. ENERGY is a state function! The energy in a system is NOT dependent on the path the system took to reach that state.
Example of State function The energy difference of a boulder between the top of a mountain and the bottom is fixed. It does not matter if a boulder rolls down the side or is carried down by a helicopter, the potential energy difference possessed by the boulder is the same regardless of the path down the mountain.
Other State Functions
Density is a state function
Temperature is a state function
density does not depend on how much matter you have.
The temperature of a piece of aluminum is independent of the amount of aluminum.
Pressure is independent of the of the container size.
NOT State Functions “dependent”
Heat and work are not state functions
The more mass you have, the more heat you have The more mass you have the more work can be done.
Temperature vs. Heat
Temperature is “Average heat” Heat is a measure of molecules in motion.
Heat may be defined as:
“the flow of energy due to a temperature difference”
The flow of energy called heat is the way in which “thermal energy” is transferred from a hot object to a colder object.
System vs. Surrounding
Exothermic = negative change in energy Endothermic = positive change in energy
EXOTHERMIC
ENDOTHERMIC
Measuring Energy Change
calorie (lower case –c-) is defined as the amount of energy (heat) required to raise the temperature of one gram of water by one degree Celsius. One Calorie (capital –C- ) is one kilocalorie …. 1000 calories. The SI unit for heat is the Joule (J). 1 cal = 4.18 Joules
Conversion from Joule to calories and calories to Joules
How many calories is 700 Joules? calorie calories 700.0J x 167.5 calories 4.18J
How many Joules is 3400.0 calories? 4.18J Joules = 3400.0 calories x 813.4 Joules cal
Specific Heat Capacity
“The amount of heat required to change the temperature of one gram of a substance by one degree Celsius.
1 cal cal The Specific heat of water is 1.000 o 1g x 1 C g Co 1 cal 4.18 J 1 cal 4.18 J i.e. or or or o o g C g C g T g T
Sp Heat of other substances units = J/g-C
Water . . . . . 4.18 Aluminum . . 0.89 Iron . . . . . . 0..45 Gold . . . . . . . 0.13 How much heat is required to raise the temperature 100.0 g of each of these from 25C to 100C?
ENERGY(kiloJoules) = s x m ΔT ΔT = 75C grams = m = 100.0g
Water: kJ= 4.18J x 100 x 75 = 31,350J (31.4kJ) Aluminum: kJ = 0.89 x 100 x 75 =6675J (6.7kJ) Iron: kJ = 0.45 x 100 x 75 = 3375J (3.4kJ) Gold: kJ = 0.13 x 100 x 75 = 975J (0.975kJ)
Laws of Thermodynamics (3) 1st Law of Thermodynamics states: “ The energy of the universe is constant” 2nd Law of Thermodynamics states: “The universe is proceeding from order to disorder . . .entropy (S) is increasing” 3rd Law of Thermodynamics states: “The entropy (S) of a perfect crystal at absolute zero is zero . . .
ENTHALPY
Enthalpy is an energy function Enthalpy is a measure of heat produced or absorbed in a chemical reaction. At constant pressure enthalpy is: ∆ Hp ∆Hp = heat
Calculation
When one mole of methane is combusted, the measured heat is 890kJ; How much heat is produced by burning 11.8 g CH4?
mol CH 4 -890kJ Joules 11.8g CH 4 x x = -654.6kJ 16.042 g CH 4 mol CH 4
Why minus?
Hess’s Law
“… in going from a particular set of reactants to a particular set of products, the change in enthalpy (heat) ∆H is the SAME whether the reactions takes place in one step or a series of steps.
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