CHEMISTRY FOR ENGINEERS (LECTURE)
Module 1 / First Semester
Ms. Ma. Junallie E. Fuentebella-Pomperada
WORK, MECHANICAL ENERGY AND HEAT
Energy โ capacity to do work or transfer heat
Work โ the energy used to cause an object to move against a force
Heat โ energy used to cause the temperature of an object to increase
WORK
- a scalar quantity (do not have directions)
- defined and measured by the product of the net force
exerted and the distance through which force moves
Formula:
๐พ = ๐ญ๐
๐๐๐๐ฝ
where W = work
F = force
d = displacement
๐ = angle between the force and the
direction of motion
Joule (J) โ common unit for work
Conversion:
๐๐ฑ = ๐ต โ ๐ or ๐๐ฑ = ๐ ๐๐ โ ๐/๐ โ ๐๐
MECHANICAL ENERGY
- the sum of an objectโs kinetic and potential energy
KINETIC ENERGY
- known as โenergy of motionโ
- the KE of a body is dependent on its mass and speed
Formula:
๐ฒ๐ฌ = ๐๐
โ๐๐๐
where KE = Kinetic Energy
m = mass
v = speed
Note:
1. The kinetic energy of a body increases as its speed
increases. Kinetic Energy (KE) is directly proportional to
Speed (v).
โข A ball rolling at 10m/s has greater kinetic energy
than it does at 5 m/s.
2. For given speed, the kinetic energy increases with increasing
mass.
โข A large truck traveling at 50 km/h has greater
kinetic energy than a small car traveling at the
same speed because the truck has the greater
mass.
Joule (J) โ common unit for Kinetic Energy (KE)
Potential Energy
- known as โenergy due to positionโ
- an object has potential energy by virtue of its position
relative to other objects
- in essence, the โstoredโ energy that arises from the
attractions and repulsions an object experiences in relation
to other objects
Formula: ๐ท๐ฌ = ๐๐๐
where PE = potential energy
m = mass
g = gravitational acceleration (9.8 m/s2)
h = height
Joule (J) โ common unit for Potential Energy (PE)
Note:
1. Potential energy may be converted into kinetic energy
and vice versa. (The forms of energy are
interconvertible.)
โข Think of a cyclist poised at the top of a hill.
Because of the attractive force of gravity,
the potential energy of the cyclist and her
bicycle is greater at the top of the hill than
at the bottom. As a result, the bicycle easily
moves down the hill with increasing speed. As
it does so, potential energy is converted into
kinetic energy. Potential energy decreases
as the bicycle rolls down the hill, but its
kinetic energy increases as the speed
increases.
The potential energy initially stored in the motionless bicycle and rider
at the top of the hill is converted to kinetic energy as the bicycle
moves down the hill and loses potential energy.
Chemical Energy
- the energy that is released during a chemical reaction or
change
- energy is required to bond atoms together and energy is
released when these bonds are broken
- can also be viewed as energy that is stored in some kind of
chemical substance
- energy is released when these substances mix together to
cause a chemical reaction
- during photosynthesis, plants convert light energy coming
from the sun into chemical energy
Module 1: Work, Mechanical Energy and Heat
