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Thermochemistry branch of chem dealing with the relationship between chemical action and heat. . Applications of Heat and Energy. Energy. All energy can be classified as either potential or kinetic . Potential energy is any type of energy that is stored .

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thermochemistry branch of chem dealing with the relationship between chemical action and heat

Thermochemistrybranch of chem dealing with the relationship between chemical action and heat.

Applications of Heat and Energy

energy
Energy
  • All energy can be classified as either potential or kinetic.
  • Potential energyis any type of energy that is stored.
  • Examples: batteries (stored chemical

converts to electrical)

  • Top of a roller coaster hill (gravitational)
  • Candy Bar (stored energy in its chemical bonds)
  • Kinetic energy – any energy from the movement of matter.
which has more heat lake erie in december of a drop of boiling oil
Which has more heat - Lake Erie in December of a drop of boiling oil?
  • Frozen Lake Erie
  • Drop of boiling oil
which has a higher temperature lake erie in december of a drop of boiling oil
Which has a higher temperature- Lake Erie in December of a drop of boiling oil?
  • Frozen Lake Erie
  • Drop of boiling oil
heat vs temperature
Heat vs. Temperature
  • Heat is the amount of energy that flows from a hotter object to a colder one.
    • It is the sum energy of all of the molecules in a substance
  • Temperature is the average kinetic energy of an object.
heat transfer
Heat Transfer
  • Heat always flows from an object with more heat (hotter) to an object with less heat.
  • Note: Something that is cold just lacks heat. There is no unit for “cold”.
  • When you feel cold, it is because you are losing heat (not gaining “cold”)
slide7
True or False: When you place ice cream in the freezer, heat is transferred from the ice cream to the freezer.
  • True
  • False
true or false when we open the window heat is transferred from your body to the air outside
True or False: When we open the window, heat is transferred from your body to the air outside.
  • True
  • False
units of heat
Units of Heat
  • Heat is measure in Joules (J).
  • (The joule is the SI unit for all types of energy.)
  • Example: when you heat a cup of tea, you use about 75,000J (or 75 kilojoules) of heat.

Joule is pronounced jewel

other units of heat
Other units of heat
  • Heat is also measured in calories (cal).
  • 1000 calories equals a kilocalorie (Cal).
  • A calorie is the amount of heat needed to raise the temperature of 1 gram of water by 1 degree Celsius.
  • Also, 1 calorie = 4.184 Joules
  • And … 1 Cal = 4.184 kJ
units of temperature1
Units of Temperature

TF = 1.8TC + 32

TK = TC + 273

a solid becoming a liquid is called
A solid becoming a liquid is called:
  • Freezing
  • Melting
  • Evaporation
  • Sublimation
  • Condensation
  • Deposition
a gas becoming a liquid is called
A gas becoming a liquid is called:
  • Freezing
  • Melting
  • Evaporation
  • Sublimation
  • Condensation
  • Deposition
a solid becoming a gas is called
A solid becoming a gas is called:
  • Freezing
  • Melting
  • Evaporation
  • Sublimation
  • Condensation
  • Deposition
a liquid becoming a gas is called
A liquid becoming a gas is called:
  • Freezing
  • Melting
  • Evaporation
  • Sublimation
  • Condensation
  • Deposition
attractive forces
Attractive Forces
  • In gases, these attractive forces are minimal.
  • In solids and liquids, the forces are strong enough to keep the materials from scattering everywhere.
  • These attractive forces also determine the melting point and boiling point of different compounds. (ex. NaCl melts at 801o C)
changes in state
Changes in State
  • Materials experience a change in state when enough heat energy is applied to break apart (or form) the attractions between molecules.
  • When intermolecular bonds are broken, heat is absorbed from the surroundings; when the bonds are formed, heat is taken from the system and released to the surroundings.
changes in state1
Changes in State
  • Different states of matter (solids, liquids, and gases) have very different properties due to attractive forces that exist between atoms.
  • To change from a solid to a liquid, for example, these attractive forces in solids must be broken so that the liquid molecules have more freedom to move. In gases, the molecules have even more mobility.
slide22
When a solid melts, heat is removed from the surrounding environment to break those intermolecular forces.
  • True
  • False
what happens at b
What happens at B?
  • Solid starts to melt
  • Liquid starts to freeze
  • Gas starts to condense
  • Liquid starts to evaporate
what happens at d
What happens at D?
  • Solid starts to melt
  • Liquid starts to freeze
  • Gas starts to condense
  • Liquid starts to boil
what happens at e moving from right to left in the graph
What happens at E moving from right to left in the graph?
  • Solid starts to melt
  • Liquid starts to freeze
  • Gas starts to condense
  • Liquid starts to evaporate
what happens at c moving from right to left in the graph
What happens at C moving from right to left in the graph?
  • Solid starts to melt
  • Liquid starts to freeze
  • Gas starts to condense
  • Liquid starts to evaporate
melting point freezing point
Melting Point / Freezing Point
  • The melting point (same temperature as freezing point) is the temperature at which a solid turns to a liquid.
  • Latent Heat of Fusion – the amount of heat needed to freeze one gram of a substance (or the heat released when one gram of a substance melts.)
  • Note: units in J/g
latent heat of fusion
Latent Heat of Fusion

Q = m x Hfus

Heat = mass x Heat of Fusion

****For ice to water: Hfus = 334 J/g

(every substance has a difference heat of fusion)

boiling point condensation point
Boiling Point / Condensation Point
  • The boiling point (same temperature as condensation point) is the temperature at which a liquid turns to a gas.
  • Latent Heat of Vaporization – the amount of heat needed to vaporize one gram of a substance (or the heat release when one gram of a substance condenses.)
  • Note: units in J/g
latent heat of vaporization
Latent Heat of Vaporization

Q = m x Hvap

Heat = mass x Heat of Vaporization

****For water to steam: Hvap = 2260 J/g

(every substance has a difference heat of vaporization)

heat graph calculations
Heat Graph calculations
  • When the graph is flat, use latent heat equations because of change of state.
  • For melting: Q = m x Hfus
  • For evaporating: Q = m x Hvap
specific heat
Specific Heat
  • Different substances absorb (and lose) heat at different rates.
  • Specific heat (SH) is the amount of heat (q) needed to raise the temperature of 1 gram of a substance by 1 degree Celsius.
heat graph calculations1
Heat Graph calculations
  • When the graph is sloped, use specific heat equations because of change of temperature
  • Q = SH x m x Temp. Change or
measuring heat changes
Measuring Heat Changes
  • A calorimeter is an instrument

used to measure heat changes.

By placing an object in an insulated

container, the heat loss can be

measured by the temperature gain

of the water.

Heat lost by object = Heat gained by water

-qobject = qwater

slide41

Chemical reactions occur so that the atoms in the elements involved attain a more stable state of being.

collision theory
Collision Theory
  • Collision theory – molecules must collide with the proper orientation and sufficient energy to react.
activation energy
Activation Energy
  • The activation energy is the amount of energy required to break the bonds between the atoms of the reactants.
condition necessary for reactions to occur
Condition Necessary for Reactions to Occur
  • Collision: Reactants must collide.

2) Orientation: The reactants must align properly to react.

3) Energy: The activation energy must be attained to react.

energy in chemical reactions
Energy in Chemical Reactions
  • Many chemical reactions also produce energy changes.
  • Definitions:
  • System – the reactants and products in the reaction
  • Surroundings – everything else around the reaction (eg air in the room, reaction flask)
heat of reaction
Heat of Reaction
  • Heat of Reaction (ΔH) – the amount of heat lost or gained in a reaction
  • Heat of Reaction: ΔH = Hproducts – Hreactants
exothermic reactions
Exothermic Reactions
  • Exothermic Reactions – energy is produced by a reaction; energy flows from the system to the surroundings
  • ΔH is negative because the reaction loses heat.
endothermic reactions
Endothermic Reactions
  • Endothermic Reactions – energy is gained by a reaction; energy flows from the surroundings into the system
  • ΔH is positive because the reaction gains heat.
h of the reaction 560kj
ΔH of the reaction = -560kJ
  • Exothermic
  • Endothermic
heat values in chemical reactions
Heat Values in Chemical Reactions
  • Heat of Reaction is a stoichiometric value and is proportional to the coefficients of the reactants and products.
  • 2H2O + 572kJ -> 2H2+ O2
  • Therefore, for every 2 moles of water that react, 572kJ of energy are required.
slide57
Presence of a Catalyst – a substance that increases the rate without being permanently changed

- lowers activation energy

slide58
Also used:

inhibitors – “tie up” a reaction so that it does not occur (opposite of a catalyst)

- preservatives

- anti-rust agents