Specific Heat and Heat of Reaction

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Energy and Heat

• Specific Heat and Heat of Reaction
• Ms. Henriksen Chemistry

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Total Energy Potential Kinetic
We will use the following units to measure
energy calorie (cal) Joule (J)
Kinetic Energy energy of motion. Potential
Energy stored energy.
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Ball speeds up
Ball slows down
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The Law of Conservation of Energy

• Energy can be neither created nor destroyed by
  ordinary means.
• It can only be converted from one form to
  another.
• If energy seems to disappear, then scientists
  look for it leading to many important
  discoveries.

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Law of Conservation of Energy

• In 1905, Albert Einstein said that mass and
  energy can be converted into each other.
• He showed that if matter is destroyed, energy is
  created, and if energy is destroyed mass is
  created.
• E MC2

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A. Temperature Heat 1. Temperature is related
to the average kinetic energy of the particles in
a substance.
2. SI unit for temp. is the Kelvin a. K
C 273 (10C 283K) b. C K 273 (10K
-263C) c. F (9/5)C 32
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Cup gets cooler while hand gets warmer
3. Heat Energy a. The flow of thermal
energy from one object to another.
b. Heat always flows from warmer to cooler
objects.
c. Heat is a process that involves the transfer
of energy
Ice gets warmer while hand gets cooler
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4. Specific Heat a. Some things heat up or
cool down faster than others.
Land heats up and cools down faster than water
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b. Specific heat is the amount of heat
required to raise the temperature of 1 g of a
material by one degree (C or K). 1) C
water 1 cal/ g C 2) C sand 0.19
cal / g C
This is why land heats up quickly during the day
and cools quickly at night and why water takes
longer.
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Why does water have such a high specific heat?
water metal
Water molecules form strong bonds with each
other therefore it takes more heat energy to
break them. Metals have weak bonds and do not
need as much energy to break them.
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How to calculate heat of a reaction
Q m x ?T x C Q change in thermal energy
heat of reaction m mass of substance ?T
change in temperature (Tf Ti) C specific heat
of substance
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c. A calorimeter is used to help measure the
specific heat of a substance.
First, mass and temperature of water are measured
Then heated sample is put inside and heat flows
into water
Knowing its Q value, its mass, and its ?T, its Cp
can be calculated
?T is measured for water to help get its heat gain
This gives the heat lost by the substance