Do Now: Hand in specific heat lab & answer the following question on “do now” sheet:. 56 grams of hot copper are added to 140 grams of water in a 92 g aluminum calorimeter causing the temperature of the water to rise from 22.0 o C to 29.5 o C. What was the initial temperature of the hot copper?
56 grams of hot copper are added to 140 grams of water in a 92 g aluminum calorimeter causing the temperature of the water to rise from 22.0oC to 29.5oC. What was the initial temperature of the hot copper?
Cwater=4180 J/(kg K) cAl=897 J/(kg K) cCu=385 J/(kg K)
=(0.14kg)(4180 J/kg/oC)(7.5oC)=4389 J
=(0.092kg)(897 J/kg/oC)(7.5oC)=619 J
(4389 J) + (619 J) + [(21.56 J/oC)(DTcu) = 0
DTcu= - (4389 J + 619 J) / (21.56 J/oC) = -232 oC
DT = Tf – Ti Ti = Tf – DT = 29.5oC – (-232oC)
Ti = 262oC
56 g Cu
92 g Al
140 g water
State of matter with fixed volume and shape. Molecules are in motion but are tightly packed and maintain their locations relative to neighboring molecules.
Measure of the total amount of kinetic energy associated with the random motion of particles plus the total potential energy associated with the intermolecular bonds
State of matter that takes on the shape of its container but has a constant volume. Although molecules are tightly packed bonds are continuously changing as they change their locations relative to neighboring molecules.
In this state of matter molecules do not form lasting bonds with neighbors and spread out to occupy all the space available. With plenty of extra room between molecules this state of matter can be compressed into a smaller volume.
At high enough temperatures particles in a gas have enough kinetic energy to knock electrons free from neutral atoms resulting in this hot soup of charged ions.
Heat is added at a uniform rate to a pot of water that starts off at room temperature. The temperature of the water is shown for the first few minutes. Sketch what you think the rest of the graph look like if the pot is left on the stove for 20 minutes
This is what the graph actually looks like. Take 3 minutes to discuss in small groups what is going on here. Would the formula Q=mcDT work for the entire 20 minutes? Why or why not?
BIG IDEA –
At the boiling point adding heat results in a change of state. As H2O changes from liquid to gas thermal energy increases but temperature stays the same!
Amount of heat required to melt 1 kg at the melting point
Heat required to melt something: Q=mHf
Heat required to freeze something: Q=m(-Hf)
Example: Adding 668 kJ to a block of ice at 0oC causes 2.0 kg to melt. What is the heat of fusion of ice?
Q=6.68x105 J m=2.0 kg Hf=Q/m=3.34x105 J/kg
Amount of heat required to change 1 kg of liquid to a gas at the boiling point.
Heat required to vaporize something: Q=mHv
Heat required to condense something: Q=m(-Hv)
Example: The boiling point of ethanol is 78oC. How much heat must be added to 750 g of ethanol at 78oC to turn it into a gas?
Hv=846 kJ/kg m=0.75 kg Q=mHv= 635 kJ