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Thermochemistry

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Thermochemistry

The study of heat changes that occur during chemical reactions and physical changes of state

Energy is the capacity

to do work

or to supply heat.

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

WoodElectric socket

Moving baseball

- Heat (q) energy transferred between samples because of differences in temperature.
Depends on particle

- speed
- number
- size
- type of particles.

- 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.

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???

- 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?

In any chemical or physical process, energy is neither created nor destroyed.

All energy can be accounted for as work,

stored energy or heat.

But it can change form

Think of your own example and write it down!!

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

- Express 60.1 cal in units of joules.
2. Express 975 J in cal and Cal.

Amount of heat necessary to change an object’s temp. 1 degree.

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?

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

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?

Hoping you get this done in about 30 min…

q = m t C

q = energy (J)

m = mass (g)

t = change in temperature (C)

q = m t C

q = energy (J)

m = mass (g)

t = (Tfinal – T initial) = Change in temp

- 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?

There is no change in temperature…

Q = mΔH

ΔH(fus) = Heat of fusion

ΔH(vap) = Heat of vaporization

- 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).

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)

- 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

Calculate the energy required to heat 25.0 g of aluminum (Cp=0.897J/gC) from

19.5 °C to 50.5 °C.

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

Any that you need me to look at with you?

Really watch your changes in temperature because that determines the sign on q.

+q = endothermic, absorbs energy

-q = exothermic, releases energy

Review the Freezing Point/Boiling Point graph from the beginning of the year.

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.

EndothermicExothermic

Δ H Vaporization =-Δ H Condensation

Δ H Fusion = -Δ HSolidification

Use q = mΔtC for sections of the graph where kinetic energy changes.

Use q = m ΔH (process) for sections of the graph

Calorimeter- devices used to measure the amount of heat absorbed or released during a chemical or physical change

System- specific area where you are focusing your attention

Surroundings – everything outside the system