In this video we're going to be looking at forms of energy the basic forms of energy
and those specifically that we'll be looking at in chemistry plus we'll be doing a simple
kinetic energy calculation and conversion of energy units. Energy is the capacity to
do work or transfer heat. The basic forms of energy are Kinetic energy and Potential
energy. Kinetic energy is the energy of motion. Potential energy is the energy of position.
If we look at kinetic energy the base formula for kinetic energy is going to be energy kinetic
equals one half times the mass times the velocity squared or often given as KE or E to the K
equals one half mv squared. In chemistry the kinetic energy we're going to be dealing with
mostly is thermal energy, energy associated with the random motion of atoms or molecules.
Potential energy, the energy of position in chemistry we're gonna be dealing with two
potential energies: chemical energy, the energy that is stored in the bonds of chemical compounds.
So when we do a chemical reaction, we're gonna be either creating or breaking bonds and there's
an energy associated potential energy in these chemical bonds. The other is electrostatic
energy. Electrostatic energy is the energy that results from the interaction of charged
particles. If we think about a positive and negative charge they're gonna be attracted
to each other. If we think about two negative charges they'll be repulsed. The equation
for this is E to the el is proportional to Q1, the charge of the first particle, times
Q2, the charge of the second particle, divided by the distance between the two particles.
When we do this calculation if the electrostatic energy is a negative then that's an attraction.
If we have a positive and negative charge we'll end up with a negative electrostatic
energy, that's an attraction. If electrostatic energy equals positive then we have a repulsion.
We would get this if we had two positive charges or two negative charges. The other basic information
we need to know about forms of energy is the SI unit of energy. The SI unit of energy is
joule given by capital J. The units for joule is 1 kg times meters squared divided by second
squared this because a joule is defined by a 2 kg mass moving at 1 m/s. If we put that
into our formula KE equals one half mass times velocity squared we come up with joules. We
also very common non-SI unit for energy, calories given as cal this is the energy required to
raise the temperature of 1 g of water from 14°C to 15°C. One calorie is equal to 4.184
J. This is a defined number and so therefore it's exact. This is important when we think
about our significant figures in these calculations. Now let's look at two simple problems. First,
a kinetic energy problem and then a conversion problem. First problem: calculate the kinetic
energy of a hydrogen atom moving at a speed of 125 m per second. Remember our formula
is going to be KE equals one half mass times velocity squared. We're gonna be looking for
kinetic energy and it tells us that we have a hydrogen atom so our mass is going to be
the mass of the hydrogen atom and our velocity they give us as 125 m/s. Now our value should
be in SI units, and this is gonna help us get all of our units in the correct value
to get joules. So a joule is remember a kilogram meter squared divided by second squared which
means that we're gonna have to get our mass into kilograms. Let's start by looking up
the mass of hydrogen. Mass of hydrogen in atomic mass units is going to be 1.0079 amus
so if we do our conversion remember we need to get the this in kilograms we'll start by
taking that multiplying it by the unit for 1.661×10 to the -24 g for a an atomic mass
unit and then we can convert grams to kilograms by using the definition of 1000 g per 1 kg.
Do our math on that and we will get 1.674×10 to the -27 kg. Now we just need to take this
value and plug it into our formula so KE is going to equal one half 1.674 times 10 to
the -27 kg times 1.125 m/s squared do our math on that and we'll come up with 1.308×10
to the -3 J. Joules are actually small energy terms so this'll often be converted to kilojoules.
We can do that simply by understanding that there's 1000 J in 1 kJ but for for this equation
we'll just leave it in joules. Alright let's look at another problem. Calculate the number
of calories in 681.4 J. Simple conversion but again many scientific disciplines still
use calories so you'll see the conversion between joules and calories quite often. So
we know that 681.4 J we're gonna need a conversion factor. We know that one calorie is defined
as 4.184 J. We can do our calculation. We get 162.9 cal. Now for this one notice that
we have four significant figures to start with since 1 cal is equal to 4.184 J by definition
that means it's an exact term which means we have as many significant figures as we
need for that value in this case they're both four so we'll have four significant figures
in our problem, 162.9 cal. You'll be doing more calculations dealing with chemical energy
and electrostatic energy later. Simple kinetic energy problems are pretty straightforward.
Just make sure you follow your units and again make sure that you remember that 1 calorie
is defined as 4.184 J when you do conversions from joules to calories or calories to joules.