This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
THERMO-CHEMISTRY
Thermochemistry
Study of the heat changes that occur during a chemical
reaction
EnergyThe capacity to do work or generate
heat
In chemistry, energy is stored
in chemical bonds
When bonds are made, energy is released. When
bonds are broken, energy is absorbed.
The main form of energy in
chemistry is HEAT!
Heat (q)Energy that is
transferred between objects that have a
temperature difference
Heat always moves from a
higher temp to a lower temp
Terms to know: universesystem
surroundings
Law of Conservation of Energy
In any process, energy is neither
created nor destroyed
Some reactions absorb energy
(heat) and some give off energy
(heat).
Exothermic Reaction
A reaction that releases heat into the surroundings
(heat exits)
Endothermic Reaction
A reaction that absorbs heat from the surroundings
(heat goes en)
Enthalpy Change (H)
Amount of heat lost or gained in a
reaction(unit = kJ)
Sign of H
Process Heat
Positive Endo-thermic
Absorbed
Negative Exo-thermic
Released
Temperature (T)
A measure of the average kinetic energy
of the particles in a substance
Heat (Q)Energy that is
transferred between objects that have a
temperature difference
Heat (Q)Is measured in Joules (J)
(or kJ)
1 kJ = 1000 J
So…how do we measure heat?
We can only measure changes in heat
(absolute heat doesn’t exist)
Specific HeatAmount of heat needed to
raise the temp of 1g of a substance 1C
gC
J
Unit =
The Heat EquationQ = mCpT
Q = heat (joules-J)m = mass (grams)
Cp = specific heat (J/g C)T = change in temp (C)
How much heat is needed to raise the temperature of 350
grams of water from 0.0°C to 25°C?
37000 Joules
A 450 gram sample of water cools from
55°C to 10.0°C. How much heat is
lost?
85000 Joules
A 15.8-gram piece of zinc increases in temperature
from 5.5°C to 6.9°C when 8.5 Joules of heat are added. What is the
specific heat of zinc?
0.38 J/g°C
calorie (cal)Quantity of heat
needed to raise the temp of 1g of pure
water 1C
How much heat is needed to increase the
temperature of 10g H2O from 35C to
45C?100 cal
1000 calories = 1 Calorie
(Calorie is the kind on food labels, etc)
1 calorie = 4.184 Joules
Calorimeter
An insulated chamber used to measure the
amount of heat absorbed or released
during a reaction
When heat energy is added, the molecules move faster and
faster, increasing the temperature
What happens when the phase is not changing:
When heat energy is added, instead of increasing the temperature (increasing the kinetic energy of the