Thermochemistry Enthalpy: change in heat. Energy and Change of State You do not have to write this...
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Transcript of Thermochemistry Enthalpy: change in heat. Energy and Change of State You do not have to write this...
Thermochemistry
Enthalpy: change
in heat
Energy and Change of State
You do not have to write this When energy is added to a solid substance, its
temperature increases until its melting point is reached. Upon the addition of more energy, the substance begins to melt.
The temperature remains the same until all the substance has melted. ****
Energy required to melt 1 gram of a substance at its melting point
Enthalpy of Fusion (Hfus)
Heating Curve: ( For Water)
Time
-20
-10
0
Heating Ice
(solid)
Melting point (°C)
Hfus
After the substance melts and if heating continues, the temperature will continue to rise until it reaches its boiling point.
۞The temperature remains the same until all the substance has boiled.***
Energy and Change of State
Energy required to vaporize 1 gram of a substance at its boiling point
Enthalpy of Vaporization (Hvap)
Time
-20
-10
0
Heating Ice
Melting Point
100
Heating Water
(liquid)
Boiling Point
Hvap
(°C)
Hfus
► ► Important Formulas to Important Formulas to Know ◄Know ◄When a substance is being heated, use the
following formula: (inclined line)
q = (m)(c)(T)
When a substance is meltingmelting or boilingboiling, use the following formula: (flat line)
q = (m) (Hfus or Hvap)
q = (m)(c)(q = (m)(c)(T)T)
(C) = Specific Heat:
- of ice = 2.06 J/g x °C
- of water = 4.18 J/g x °C
- of steam = 2.02 J/g x °C
q = (m) (q = (m) (HHfusfus or or HHvapvap))
Enthalpy Values for Water:
Hfus = 334 J/g
Hvap = 2260 J/g
Sample Problem #1How much heat is required to melt
5.67g of ice?
Q = (m)(ΔH fus)
Q = (5.67g)(334 J/g)
Q =
Sample Problems
2.) How much energy is required to boil 85g of water?
3.) How much energy is required to convert 40g of ice at -10°C to steam at 150°C ?
4.) What is the final temperature when 1250 J of energy is added to 15g of water at 25°C ?
Sample Problem #5
How much energy is required to raise the temperature of 25g of water from 15°C to 75°C ?
Practice Problems
6.) How much energy is required to boil 50 grams of water?
7.) What is the final temperature when 2500 J of heat is added to 35 grams of water at 15 degrees Celsius?
8.) How much energy is required to convert 75 grams of ice at -20 degrees Celsius to steam at 125 degrees Celsius? (Hint: This problem has 5 steps!!)