Heat, represented
by q, is energy
What is temperature?
that transfers from one object to
A measure
of the
kinetic
another
because
ofaverage
a temperature
energy of between
the particles
of a sample;
difference
them.
how fast the particles are moving
Heat flows from a warmer object to a cooler
object until the temperature of both objects is
the same. Consider a glass of ice water.
Calorie = Quantity of heat needed to raise
the temperature of 1 g of pure water by 1
degree Celsius.
1 Cal = 1000 cal = 1kcal
1cal = 4.184 Joules (a unit of heat and energy)
Example 10.1
Express 60.1 cal of energy in units of Joules.
Phase Change: a change in the form of a substance
that affects the speed of the particles, the strength of
intermolecular forces*, and proximity of the particles; the
composition of the substance is NOT affected.
• Endothermic phase changes
•Melting
•Vaporization
• Exothermic phase changes
• Condensation
• Freezing
Forces of attraction that form between two
separate molecules usually due to polarity
• Polarity = electronegativity
difference leaving partial
charges on the atoms
• Notice the FIVE water
molecules in the picture
•The dashed lines show
attractions between opposite
partial charges on different
water molecules.
Solid
KE of particles
Temperature
Liquid
KE of particles
Temperature
Gas
KE of particles
Temperature
Strength of IMF Strength of IMF Strength of
IMF
Proximity of
particles
Proximity of
particles
Proximity of
particles
•
•
Endothermic changes in enthalpy
•
Will the measurement be positive or negative?
•
Will a graph of energy change end higher or lower
than it began?
•
Is this considered heating or cooling a substance?
Exothermic changes in enthalpy
•
Will the measurement be positive or negative?
•
Will a graph of energy change end higher or lower
than it began?
•
Is this considered heating or cooling a substance?
1. Number the line segments starting at the left.
2. Label the states of matter and phase changes.
3. Label the segments that represent temperature changes
with ∆T.
4. Label the segments that represent NO temperature
changes, but instead show only changes in heat content,
with ∆H.
* Sometimes heat enters a system and changes the KE (temp), but other
times heat enters a system to make other changes (enthalpy).
1. Label the graph with equations that can be used to calculate
the heat involved at EACH segment.
2. Select segments to label with q = m c ∆T
3. Select segments to label with q = mol ∆H
•
Use the graph to substitute values for ∆T.
•
Use constant values for c. (c differs with substance.)
•
Use constant values for ∆H. (∆H differs with substance.)
Quantities will be
given in the problem.
Heat of fusion= heat absorbed by one
mole of a substance in melting from a
solid to a liquid at STP
Heat of solidification=heat released
by one mole of a liquid as it solidifies
at STP
ΔHfus = - ΔHsolid
Quantities will be
given in the problem.
Heat of vaporization= heat absorbed
by one mole of a substance vaporizing
at STP
Heat of condensation=heat released
by one mole of a gas as it condenses at
STP
ΔHvap = - ΔHcond
Water
c = 4.184 J/g°C
∆Hfusion = 6.02 kJ/mol
∆Hvaporization = 40.6 kJ/mol
Example 14.1
Calculate the energy required to melt 8.5 g of ice at 0°C.
Example 14.2
Calculate the energy (in kJ) required to heat 25 g of liquid
water from 25°C to 100°C and change it to steam at
100°C.
Section Review Question 7
Calculate the energy required to change 1.00 mol of ice
at -10°C to water at 15°C.
A phase diagram gives the conditions of
temperature and pressure at which a
substance exists as solid, liquid, and gas.
•Each of the three regions represents a pure
phase (not a mix).
•Each line represents the temp & pressure
conditions where the phases exist in equilibrium.
•Triple point: set of conditions in which all
phases exist in equilibrium
Amount of heat required to raise 1 g of
the substance by 1 degree Celsius.
The units of specific heat are J/gºC or cal/g ºC. These
numbers can be found on a table on pg. 329. The
numbers are calculated by using
q = m c ΔT
Example 10.4
A 1.6g sample of a metal that has the appearance of gold requires
5.8 J of energy to change its temperature from 23°C to 41°C. Is
the metal pure gold?
Specific Heat WS (Practice Packet)
1. A 15.75-g piece of iron absorbs 1086.75 J of heat energy, and
its temperature changes from 25°C to 175°C. Calculate the heat
capacity of iron.
Heat flows from _______ to ________ until
equal _______________________ is reached.
In the glass of water, the
substance gaining heat is
theoretically getting it from the
warmer substance. So, if 456 J
of heat is lost from the warm
substance, how many joules are
gained by the cool substance?
What if the system is NOT
insulated from other heat
sources?
q lost + q gained = 0
Calorimeter
A calorimeter is an insulated instrument that uses water
making heat calculations more accurate.
A 25.0 g sample of pure iron at
85°C is dropped into 75 g of
water at 20°C. What is the final
temperature of the water-iron
mixture?
In a calorimeter, we KNOW that
heat lost by the warmer object
equals heat gained by the cooler
object.
Calorimeter
q lost + q gained = 0
Chemistry Thermo WS of Practice
Problems
16. The specific heat capacities of Hf and
ethanol are 0.146J/gC and 2.45J/gC,
respectively. A piece of hot Hf weighing 15.6
g at a temperature of 160.0C is dropped into
125 g of ethanol that has an initial
temperature of 20.0C. What is the final
temperature that is reached, assuming no
heat loss to the surroundings?
So far, we’ve been analyzing temperature changes and
calculating the heat involved in these PHYSICAL
changes.
Now, we are going to transition back to chemical
changes...chemical reactions. Look at the reaction
described below:
2S + 3O2 --> 2SO3
∆H = -791.4 kJ
Analyze the reaction:
1. Is heat absorbed or released?
2. What conversion factors could be written to include the
heat?
The reaction could also be written in this form:
Original:
2S + 3O2 --> 2SO3
∆H = -791.4 kJ
2S + 3O2 --> 2SO3 + 791.4 kJ
Calculations:
How much heat will be released when 6.44 g of sulfur
reacts with excess O2 according to the equation above?
Let’s also learn to draw/interpret a graph to represent
roughly how the energy has changed during this reaction.
Let’s look at the 12-2 Practice Problems
in your packet.
You only need a balanced chemical
equation to do stoichiometry.
We’ve done #1 together. Begin with
question 2 and complete the handout.
Prove your knowledge of Stoichiometry and
Heat BEFORE visiting the review stations:
• Solve the even questions on 12-2 Practice
Problems.
• Solve the stoichiometry handout questions.
• ½ assignment: 12-2 #2,6,10 & even handout
AFTER CONFIRMING ANSWERS WITH
MRS. TARVIN, YOU MAY GO TO THE
REVIEW STATIONS.
A sample of silver with a mass of 63.3 g is heated
to a temperature of 111.4ºC and placed in a
container of water at 17ºC. The final temperature
of the silver and the water is 19.4°C. Assuming no
heat loss, what mass of water was in the
container? The specific heat of water is 4.184
J/gºC, and the specific heat of silver is 0.24 J/gºC.
A 133g piece of granite rock is heated to
65.0°C, then placed in 643g of ethanol at
12.7 °C. Assuming no heat loss, what is the
final temperature of the granite and ethanol?
cgranite = 0.8J/gºC and cethanol = 2.44J/gºC
1. Work the problems suggested on last week’s
calendar.
2. Complete the short answer first. This section
is worth 54.5 points. Spend no more than one
hour on this section.
3. There are NO calculations in the multiple
choice section. The 13 questions are conceptbased, and they count 3.5 points each.
4. Check the multiple choice answers...your
careless mistakes cost the most.
Let’s begin our new unit on “Solutions.” Remember, a
solution is simply a homogeneous mixture of substances.
Notice: The lab area contains two stations for each
learning style: Visual, Kinesthetic and Auditory.
Instructions:
1. Take a clean piece of paper and a pencil to your first station.
2. Find the HOT PINK sign for your style’s first station. Use the
instructions and materials at the station to begin building your
basic understanding of graphs called Solubility Curves.
3. When you are done with station one, move on to your style’s
second station. Use the instructions and materials to apply
your basic understanding.