Fundamentals Of Energy

Question 1

What is energy ?

Answer 1

Energy is the ability to do work or produce heat

Question 2

Write all you know about kinetic energy

Answer 2

Kinetic energy =1/2 (mv^2)
Kinetic energy is energy that represents anything moving .
Kinetic energy is always written in joules (J).
1joule = 1kgm^2*s^2.

Eg. If the mass of a car is 10kg and moves at a velocity of 5meters per second find the kinetic energy.
KE= 1/2(10kg(5m/s)^2)
KE= 1/2(10kg(25m^2/s^2)
KE= 1/2(250kgm^2/s^2)
KE =125kgm^2/s^2= 125J

Question 3

All about potential energy

Answer 3

Potential energy is energy energy from a position above ground level. It is represented by the formulary PE=mgh
M = mass (kg),g= gravitational acceleration which is always equal to 9.8m/s^2 and h= height from the ground (m) .

Note that as object A begins to fall to the ground The potential energy decreases and the kinetic energy increases. Right before the object hits the ground at position B the potential energy is equal to the kinetic energy.

So is PE = 4900J right before it hits the ground KE=4900J

Question 4

What does this statement mean : kinetic energy +potential energy = constant.

Answer 4

This means that despite the influence on either energy such as gravity and velocity the sum of both remains the same .

Question 5

What is system and surroundings ?

Answer 5

A system is the part of the universe we are interested in all other parts are called surroundings

Question 6

How many types of systems are there name and define them

Answer 6

Open system : it can exchange energy and molecules (matter) with the surroundings.
Closed system : it can only exchange energy with the surroundings not molecules (matter) .
Isolated system: it can neither exchange molecules (matter) or energy with the surroundings.

Question 7

What is internal energy? Note down all there is to know about internal energy.

Answer 7

Internal energy refers to the total energy a system has .
The internal energy is the sum of kinetic energy and potential energy of molecules in a system.
Usually represented by either U or E.
The total value of internal energy is hard to determine so we focus on the change in internal energy (🔼U)

Question 8

Is this true or false: energy can neither be created or destroyed . It can however be transformed from one form to another and it can also be stored.

Answer 8

True

Question 9

Write all there is to know about the The first law in thermo dynamics

Answer 9

The 1st law is an unproven assumption (postulat) .
The law states the the internal energy of a system changes when there is change in flow of energy or heat (or both).
🔼U = Q+W
Where Q is heat and W is work.
W is positive if energy is transferred into the system by work and Q(heat ) is positive if energy is transferred into the system by heat.

Energy that is moved out of the system by both W or Q is negative.

So can also be depicted by 🔼U =Uafter -Ubefore.

Question 10

Determine the 🔼U of a system where 15.6KJ flows into the system by heat and 1.4KJ of work is done in the system .

Answer 10

🔼U = Q+W
(Heat)Q=+15.6KJ
(Work)W = +1.4KJ
🔼U= +15.6+1.4 = 17.0KJ
So the internal energy of the system increases by 17.0KJ

Question 11

Write what there is to know about efficiency

Answer 11

Finding efficiency is equivalent to finding how efficient a system is at converting energy in one form into useful energy in another form..

Energy in a system = useful energy delivered + energy wasted.

So then Efficiency = useful energy delivered/ energy input

Question 12

A power plant receives 100units of energy and loses 65 units of energy . What is the efficiency of the power plant? Check slide 12again for revision of how to calculate overall efficiency.

Answer 12

Efficiency = useful energy delivered/energy input
Energy input = 100units
Useful energy delivered ?

Energy into the system = useful energy delivered +energy wasted
Useful energy delivered = energy into the system - energy wasted = 100-65
Useful energy= 35
Efficiency = 35/100=0.35

Question 13

Write all there is to know about the second law of thermodynamics

Answer 13

This law determines if a process is spontaneous eg. A ball rolling down a hill is spontaneous but not up the hill. A system changing energy forms from hot to cold is spontaneous but not the other way around.

Entropy= S

🔼Suniverse = 🔼Ssystem +🔼Ssurrounding.

For a spontaneous process 🔼Suniverse >0

For a spontaneous process in an isolated system 🔼Ssystem >0

Question 14

Units of energy and the conversion between them.

Answer 14

FORCE= mass(kg)acceleration(m/s^2) = Kgm/s^2
It can als be written as Newton because 1kgm/s^2= 1(N)Newton.
ENERGY= force(N or Kgm/s^2)distance(m) this used when the question involves finding the energy of a moving object.
E=f*d meaning E=Nm /Kgm^2/s^2. Or Joules.
1Joule= 1Nm
POWER = energy(J or Nm or kg.m/s^2) /time(s).
Power= J/s or Nm/s or Kgm/s^3. Power,s SI unit is Watt(W)
So 1W=1J/s

VIP!
Energy is ultimately expressed as E= power time (used when finding the energy of a stationary object using power)
E(joule)=Wattsecond so then 1joule =1W/second.
Relation ship between Wh and J
1wh
H= hour=3600seconds so 1wh= 3600Ws . However 1Joule = 1Ws
So ultimately 3600Ws = 3600 joules. Which makes 1wh=3600j

1killowatt= 1000j/s

You’ll know which energy formulas to use depending on if watts or Newton is used in the question.

Question 15

Common unit prefixes for kilo, mega, giga, Tera, peta

Answer 15

Kilo (K)=10^3
Mega (M) = 10 ^6
Giga (G) = 10 ^ 9
Tera (T) = 10^ 12
PETA (P) = 10 ^15

Question 16

Calculate this : a house consumes on average 2kw of electricity. Calculate the energy consumed during one year in KWh.

Answer 16

Energy = Power * time
Power = 2Kw
Time = 365 days*24h= 8760h
Energy= 2Kw * 8760h
E= 17500kwh

Question 17

Why is it not likely potential energy to be directly equal to kinetic energy ?

Answer 17

Heat loss during transformation is what cause the two be unequal.

Question 18

What is the specific heat capacity ?and what is the SI unit .

Answer 18

Specific heat capacity is how much energy is required to heat up a substance. J K^-1g^-1 (heat capacity per gram of a substance).

Question 19

Is the specific heat capacity of water high and why is it high ?

Answer 19

The specific heat capacity of water is very high . This high specific heat capacity csn be attributed to the large number of hydrogen bonds in water molecules. Hydrogen bonds are considerably harder to break hence the need for for high heat.

Csp(Specific heat capacity)
Csp,H2O= 4.18JK^-1g^-1

Question 20

What is the formulae for specific heat capacity ?

Answer 20

Csp= Q/m*🔼T

Q= heat
M= mass
🔼T= change in temperature

Question 21

Is the following true when ther is kinetic energy there is also potential energy ?

Answer 21

True

Question 22

Write what you know about PCM (phase change materials).

Answer 22

Phase change materials can act as thermal batteries. Eg. This means that when a solid substance melts it absorbs and stores heat and when it goes back to its solid state (freeze) it releases energy .

Question 23

What is electrical energy?

Answer 23

Electrical energy being present in a material simply means that electrons are moving within the said material.

Question 24

What are some stuff to note about electrical energy ?

Answer 24

U = R*I
U = voltage ( v)
R= resistance (ohms )
I= current ( A amphere)

Question 25

How is electrical energy calculated?

Answer 25

Electrical energy can be calculated in two ways :
Using direct current and alternating current.

Direct current :
First find power = U * I = watt
Where U = voltage and I current

Since energy can be calculated with : Energy = PT
Energy = UI*T unit will be in joules.

Electrical energy in an alternating circuit formula is much more complicated .

Question 26

What is chemical energy ?

Answer 26

Chemical energy can be referred to as energy that is released or store when a chemical reaction occurs.

Question 27

Formula for entropy of reaction(🔼Hreaction)

Answer 27

Entropy of reaction (🔼Hreaction)= sum 🔼Hf pollutants - sum of 🔼Hf reactants
Unit= Kj/mol

Revise the slide again

Question 28

Write all you know about nuclear energy

Answer 28

Nuclear energy can be categorized into two fission and fusion.

Fission : this is a nuclear reaction where the atom of a nucleus splits into two or more separate nuclei.
This reaction produces gamma rays and releases large amount of energy.