Transcript Thermo PPT#1 - Rothschild Science

Thermochemistry
The study of heat changes
that occur during chemical
reactions and physical
changes of state
What is energy?
Energy is the capacity
to do work
or to supply heat.
Kinds of Energy
Potential energy- stored energy
Kinetic energy- energy of motion
Chemical potential energy- energy stored
within the bonds of compounds.
Radiant energy- energy from the sun
TPS- Classify the Type of Energy
Wood
Moving baseball
Electric socket
What is the difference between
Heat and Temperature?

Heat (q) energy transferred between samples
because of differences in temperature.
Depends on particle
• speed
• number
• size
• type of particles.
What is the difference between
Heat and Temperature?

Temperature is a measure of the average
kinetic energy of molecular motion in a
substance.
Temperature does not depend on
the size or type of object.
Increasing/Decreasing Temp
Adding Heat (energy) increases temperature
and increases kinetic energy .
Higher temperatures mean that the molecules
are moving, vibrating and rotating with more
energy.
What would removing heat do???
Energy (Heat) Transfer

What happens if we bring two objects that are the
same temperature in contact?

Now, what happens to the temperature if one object
has a higher temperature than the other?
Law of Conservation of Energy
In any chemical or physical process, energy is
neither created nor destroyed.
All energy can be accounted for as work,
stored energy or heat.
Warm Up- Think about the types of energy(kinetic,
potential and chemical potential.
But it can change form
Think of your own example and write it down!!
Measuring HeatImportant conversions
Cal = (C) Food Calorie
calorie = (cal) scientific calorie, amount of heat needed to
raise 1g of water 1 degree C.
Joule = (J) SI unit of heat and energy
1 Cal = 1000cal = 1kcal = 4186J
1J = 0.239 cal
Try these!
1.
Express 60.1 cal in units of joules.
2. Express 975 J in cal and Cal.
Heat Capacity
Amount of heat necessary to change an
object’s temp. 1 degree.
Specific Heat Capacity (C) or (Cp)
The amount of heat it takes to raise the
temperature of 1g of the substance 1C.
Helps you determine how much energy it takes to
heat an known mass of a substance from one
temperature to another.
How much energy would it take to heat 50g of
water from 50C to 100C?
Specific Heat Capacity (C) or (Cp)
Water- 4.2 J/gC
Alcohol- 2.4 J/gC
Wood- 1.8 J/gC
Aluminum- 0.90 J/gC
Glass- 0.5 J/gC
Check out the units!
These are the key to upcoming problems
What do you remember about
Direct and Indirect Proportions?
Two quantities are directly proportional if
dividing one by the other gives a constant
value.
Y =k
X
What would the graph look like?
Two quantities are inversely proportional if
their product gives a constant value.
XY = K
What would the graph look like?
Work on the POGIL
Hoping you get this done in about 30
min…
Specific Heat Capacity
q=mtC
q = energy (J)
m = mass (g)
 t = change in temperature (C)
Specific Heat Capacity
q=mtC
q = energy (J)
m = mass (g)
 t = (Tfinal – T initial) = Change in temp
Doing specific heat problems
1.
2.
3.
Write the equation q = m  t Cp
Manipulate equation to solve for
the variable you want.
Plug the known values into the
equation.
Simple Huh?
During a phase change…
There is no change in temperature…
Q = mΔH
ΔH(fus) = Heat of fusion
ΔH(vap) = Heat of vaporization
Example Problem 1

How much energy is required to raise
the temperature of 15g of water from
25C to 75C? (The specific heat capacity
of water is 4.18J/gC).
Practice 2- Do the problem and
discuss the process with your partner.
A particular sample of iron requires 562 J to raise
it’s temperature from 35.0 °C to 70.0 °C. What
is the mass of the sample? (Cp of iron is
0.449J/gC)
Problem 3

If 100 J of heat energy is applied to 75g
of mercury (Cp=0.140J/gC). How much
will the temperature of mercury
increase?

What is the final temperature if the initial
temperature is 45 °C
Problem 4
Calculate the energy required to heat 25.0
g of aluminum (Cp=0.897J/gC) from
19.5 °C to 50.5 °C.
Warm Up
You have 10 minutes to finish the POGIL
and/or the Copper Lab calculations.
Flip your POGIL to p.2 before turning it in.
Paper Clip your lab teams packets togthr
Homework
Any that you need me to look at with you?
Energy Values
Really watch your changes in temperature
because that determines the sign on q.
+q = endothermic, absorbs energy
-q = exothermic, releases energy
Energy in changes of state…
Review the Freezing Point/Boiling Point graph
from the beginning of the year.
What is happening with Energy
When the graph is increasing temperature,
kinetic energy is changing because the
molecules are moving faster.
When the graph plateaus, energy is still
being absorbed, but it is being used to
break intermolecular forces… potential
energy is changing.
Remember…. The Processes
Endothermic
Δ H Vaporization =
Δ H Fusion
=
Exothermic
-Δ H Condensation
-Δ HSolidification
To Calculate the change in
Energy…
Use q = mΔtC for sections of the graph
where kinetic energy changes.
Use q = m ΔH (process) for sections of the
graph
How can we measure the
energy?
Calorimeter- devices used
to measure the amount
of heat absorbed or
released during a
chemical or physical
change
Important Vocabulary Terms
System- specific area where you are focusing
your attention
Surroundings – everything outside the system