Download Energy Changes in Molecular Levels

D.S.Q.
January 25, 2016
 1. A common liquid, hydrogen peroxide, can be created
by mixing water with oxygen. Do you think this would
be a chemical or physical change? Explain
 1. A common liquid, hydrogen peroxide, can be created
by mixing water with oxygen. Do you think this would
be a chemical or physical change?
 1. A chemical change because the elements rearrange
to form a new substance
DSQ
February 27, 2017
What Is kinetic energy?
What is potential energy?
 Kinetic is energy in motion
 Potential is stored energy
PHET Website Activity
NOTES!
 Review:
 Energy is the ability to cause change
 What is potential energy?
 Stored energy due to the interaction between
objects or particles
 Energy is measured in Joules (J)
Potential Energy
Kinetic Energy
 What is kinetic energy?
 Energy due to motion
 Energy is always measured in Joules
 All objects that have motion, have kinetic energy
 K.E. is related to the mass and the speed of an
object.
Mechanical Energy
 Is the sum of the potential energy and the kinetic
energy in a system.
 For example, if the P.E. is 10 J and the K.E. is 30 J.
What is the mechanical energy?
Law of Conservation of Energy
 Energy can be transformed from one form to
another but it cannot be created or destroyed.
 What happens when a tennis player hits the ball with
the racket? (Think about the diff. energies)
Kinetic Molecular Theory
 3 major parts:
1. All matter is made of particles
 2. Particles are in constant, random motion
 3. Particles constantly collide with each other and
with the walls of their container
 http://lab.concord.org/embeddable.html#interactives
/sam/phase-change/6-phase-changes-caused-byenergy-input.json
Temperature
 The temp. of something depends on how much
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kinetic energy the particles that make up the material
have
The measure of the average kinetic energy of the
particles in a material is called temperature
If anything has little kinetic energy, the object has low
temperature
The SI unit for temperature is Kelvin (K) or some
scientist use Celsius
The higher the temperature, the quicker the
molecules and particles move and collide
Thermal energy
 The sum of P.E. and K.E. of the particles that
make up an object
 The transfer of thermal energy between materials
depends on the movement of the particles in a
material
 Remember thermal energy moves from hot
materials to cold materials
Thermal Equilibrium
 What happens if you leave a water bottle in the fridge
for several hours?
 The temperature of the water, the bottle and the air in
the fridge become the same
 When the temperatures of materials that are in
contact are the same, the materials are said to be
in thermal equilibrium.
Heat Transfer
 How is thermal energy transferred to the water in this
image below?
Conduction
 Fast moving particles of the gases in the flame
collide with the particles that make up the pan.
 Thermal energy is transferred to the pan
 Conduction is the transfer of thermal energy by
collision between particles in matter

Radiation
 The side of the pan is warm due to thermal energy
being transferred
 The transfer of thermal energy by electromagnetic
waves is known as radiation
Convection
 IS the transfer of thermal energy by the movement of
the particles from one part of a material to another is
known as convection
 The particles from the top of the water, sink to the
bottom of the pan and the water at the bottom of
the pan, float to the top.
 Changes from a solid to a liquid is
called melting point
 Changes from a liquid to a gas is called
vaporization
 Liquids vaporize in two ways; boiling or
evaporation
Conductors & Insulators
 When you put a pan on the stove, the pan gets really
hot. However, why doesn’t the handle get hot?
 The metal that makes up the pan is a thermal
conductor, a material in which thermal energy
moves quickly
 The material that make up the pan’s handle is a
thermal insulator, which is a material in which
thermal energy moves slowly
When you heat a solid, the
molecules…
 Gain energy
 Move faster
 Collide harder and more often
 Spread apart
 The cohesion becomes less and the solid turns
into a liquid
When you heat a liquid, the
molecules…
 Gains energy
 Moves even faster
 Collide more often and harder
 Spear apart
 The molecules lose all cohesion and the liquid
becomes a gas
When a gas is cooled, the
molecules
 Lose energy
 Move slower
 Collide less often and softer
 Come together
 The molecules gain cohesion and become a liquid
When a liquid is cooled, the
molecules
 Lose energy
 Move slower
 Collide less often and softer
 Come together
 The molecules gain much cohesion and become a
solid
Sublimation
When a solid goes straight to
a gas, skipping the liquid
phase
Example dry ice
Deposition
When a gas goes straight to
a solid, skipping the liquid
phase
Ex. Frost
DSQ
March 1, 2017
 1. What is dry ice made from?
 2. What is process called when matter changes from a
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solid to a gas?
3. What is the process called when matter changes
from a gas to a solid?
1. Frozen carbon dioxide
2. Sublimation…ex. Dry ice
3. Deposition… ex. Frost forming on an object