Specific heat

Objective 11D
Specific heat
• The amount of heat per unit mass
required to raise the temperature by one
degree Celsius.
• The higher the specific heat, the more
energy a substance can absorb.
• Water’s specific heat is 4.18 J/goC
Calculating energy from
specific heat
• As heat is added to a system, the
temperature increases; increasing the
energy in the system.
• The formula used to calculate the energy
in the system is:
Q = mcΔT
ENERGY
MASS
SPECIFIC
HEAT
TEMPERATURE
CHANGE
Examples:
How many energy is
needed to heat
10.0grams of water at
40oC to 65oC?
If it takes 3500J of
energy to raise the
temperature of water
from 23oC to 79oC,
what is the mass of the
water?
Q = m c ΔT
Q = m c ΔT
X=(10g)(4.18J/goC)(25oC)
3500J=(X)(4.18J/goC)(56oC)
X= 1045 J
X= 14.95g
Classroom Problem #1
36g of copper, gains 265J
of energy. What was its
change of temperature?
Substance
Aluminum
Calcium
Copper
Gold
Iron
Mercury
Silver
Specific Heat
0.90 J/goC
0.65 J/goC
0.39 J/goC
0.13 J/goC
0.46 J/goC
0.14 J/goC
0.24 J/goC
Classroom Problem #2
36.00 g of gold was
heated from 20.0oC to
22.0oC. How much
energy was added to
the gold?
Substance
Aluminum
Calcium
Copper
Gold
Iron
Mercury
Silver
Specific Heat
0.90 J/goC
0.65 J/goC
0.39 J/goC
0.13 J/goC
0.46 J/goC
0.14 J/goC
0.24 J/goC
Classroom Problem #3
An 16.0-g piece of an
unidentified metal was
heated from 1.5oC to
19.0oC, absorbing182J
of heat energy. Identify
the metal.
Substance
Aluminum
Calcium
Copper
Gold
Iron
Mercury
Silver
Specific Heat
0.90 J/goC
0.65 J/goC
0.39 J/goC
0.13 J/goC
0.46 J/goC
0.14 J/goC
0.24 J/goC
Homework Obj.11D
1. An 18.0-g piece of an unidentified metal was
heated from 21.5oC to 89.0oC. If 170J of heat
energy was absorbed by the metal in the heating
process, what was the specific heat of the metal?
2. If the specific heat of water is 4.18J/goC, what is the
amount of heat energy required to change 15.0
grams of water at 0oC to water at 100oC?
3. 96.00 g of gold was heated from 20.0oC to 220.0oC.
How much energy was added to the gold (0.13
J/goC)?
4. How much heat is needed to change the
temperature of a 33-gram sample of copper from
2.7 ºC to 162.3 ºC (0.39 J/goC)?
OBJECTIVE 11E
CATALYSTS ALLOW A REACTION TO PROCEED
WITH A LOWER ACTIVATION ENERGY.
Heating curves display the
temperature and state of matter for
a substance.
Changes in temperature require use of
the specific heat formula.
Q = mcΔT
• How much energy is required to change
10 grams of water at 50oC to 80oC?
(c = 4.18 j/goC )
Heat of fusion is the amount of energy it
takes for 1 gram of a substance to change
from solid to liquid or liquid to solid.
E = (m) (Hf)
How much energy is required to melt 10
grams of ice?
(heat of fusion for water is 334 J)
Heat of vaporization is the amount of
energy it takes for 1 gram of a substance
to change from liquid to gas or gas to
liquid.
E = (m) (Hv)
How much energy is required to boil 10
grams of water?
(heat of vaporization for water is 2257 J)
Crossing the States: if both
temperature and phase changes occur,
use all formulas that apply.
• How much energy is required to change
10 grams of ice at -50oC to steam at
180oC?
Homework
1. How much energy is needed to melt 34grams
of ice? (Hf = 340 J/g)
2. How much energy is needed to vaporize
57grams of water? (Hv = 2240 J/g)
3. How much energy is needed to raise the
temperature of 100grams of ice from 0oC to
water at 50oC? (remember: c = 4.18J/goC)
4. How much energy is needed to raise the
temperature of 100grams of ice from -20oC to
water vapor at 120oC?
QUESTIONS YOU HAVE, ASK
NOW YOU SHOULD.
Objective 11DE Test : April 4-5

Download Report