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CHEM 120 / CHEM120 Week 6 Concepts GRADED A+
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Week 6 Concepts: Nuclear Chemistry, Energy, and BiochemistryLAWS OF THERMODYNAMICS
In this section, we explore the rules of energy that we observe in the
universe. We see many examples of these laws in action on a day-to-
day basis. You will learn how to compare and contrast exothermic
and endothermic reactions as well as the first and second laws of
thermodynamics.
1. Which of these would you classify as an exothermic process?
o Evaporation of alcohol
o Photosynthesis
o Wood burning
o Ice melting
2. Which one of these processes would NOT be possible?
o Energy is transferred in a chemical reaction
o Energy is created in a chemical reaction
o Two liquid chemicals are mixed together, and the temperature of the mixture rapidly cools
o Energy spontaneously flows from a hot object
Energy cannot be created or destroyed in a chemical reaction.
ENERGY AND FIRST LAW OF THERMODYNAMICS
Energy takes many forms. A few of the more common forms of energy we observe are light, heat,
mechanical energy, and electricity. Energy is the driving force of this universe and necessary for all life,
light, and movement. Energy can be measured using various units, including calories and joules.
A good starting point in understanding the flow of energy is the First Law of Thermodynamics:
Energy in an isolated system cannot be created or destroyed, only transferred.
This law is often also known as Conservation of Energy, as this law tells us that energy is conserved and
simply moved from one place to another and one form to another. For example, when you drive a car
down the road, you are converting the chemical energy found in gasoline into heat and kinetic
(movement) energy. None of this energy is destroyed or eliminated in this process.
As another example of the first law of thermodynamics in action consider a falling stone hitting the
earth. The kinetic energy of this stone is converted mainly into sound, and vibration. In both of these
examples, we see that energy can move from one form to another.
You may have noticed the term “isolated system” in the 1st Law of Thermodynamics. This term means a
system where no matter and no energy go into or out of the system. Our universe, as we understand it, is
an example of such a system, so this law applies to our universe.
SECOND LAW OF THERMODYNAMICS
The second law of thermodynamics tells us about how energy in the universe
behaves in terms of flow and organization.
,Week 6 Concepts: Nuclear Chemistry, Energy, and Biochemistry
The amount of entropy in an isolated system irreversibly increases over time.
This law tells us that the amount of entropy, or disorder, in the universe is constantly increasing. An
important reason for this is that heat spontaneously and irreversibly transfers from a hot body to a cold
body. An example that illustrates both of these points is a cup of hot coffee sitting outside on a cold
winter's day. At first, the heat is localized into the area of the liquid in the cup; however, the heat quickly
begins to disperse into the surrounding environment spontaneously. Over time, the coffee in the cup will
have the same temperature as the surrounding environment as the temperatures even out. In this way,
we see that:
Heat was spontaneously and irreversibly transferred from a higher temperature system area to
the lower temperature surroundings.
Disorder increased as the localized heat spread through the surroundings.
3. For each of the situations, determine if the observed behavior is a consequence of the first or
second Law of Thermodynamics:
Situation Select Law
As a rocket takes off, energy in the fuel is converted into kinetic
1st Law of Thermodynamics
energy, heat, and light.
An ice cube melts on a hot day. 2nd Law of Thermodynamics
On a hot day, you turn on the oven, causing the room to become
2nd Law of Thermodynamics
even hotter.
Turning on a computer results in electricity being converted into
1st Law of Thermodynamics
mechanical work, heat, and light.
ENDOTHERMIC AND EXOTHERMIC REACTIONS
Energy can flow into a system from the surroundings or from the
surroundings into the system. The terminology we use for these
processes is:
Exothermic: Energy from system to surroundings (energy
released)
Endothermic: Energy from surroundings to system
(Energy absorbed)
The image illustrates this process. We often measure this energy
in the form of heat, so heat flowing from the system to the
surroundings is considered exothermic, while heat flowing into the system is considered endothermic. A
good mnemonic is that exo = exit (energy exits).
An example of an exothermic process is a burning match. The burning match releases heat into the
surroundings and is thus classified as exothermic. On the other hand, you may have used a chemical
cooling pack to treat an injury. In a chemical cooling pack, the chemical reaction absorbs heat from the
surroundings, cooling your injury. Since energy is going from the surroundings to the system, we would
consider this process endothermic.
,Week 6 Concepts: Nuclear Chemistry, Energy, and Biochemistry
What about ice melting? Would you consider this to be endothermic or exothermic? Is energy going in,
or is energy going out?
Ice melting is endothermic as energy goes into the ice, giving the molecules of water the energy they
need to move more quickly. This transforms the solid. As a material absorbs energy (endothermic), the
atoms and molecules in the material move more quickly and the state of the material changes from solid
to liquid to gas. Opposingly, as a material releases energy (exothermic), the atoms and molecules slow
down, moving from gas to liquid to solid.
4. Match the reaction to the type:
o Endothermic
o Photosynthesis
o Chemical ice packs
o Methanol evaporating
o Iron melting
o Exothermic
o Water freezing
o Burning gasoline
o Water condensing on a cool surface
o Two chemicals are mixed together, producing heat
5. When a cool penny is placed in a hot car in the summer, the heat flows spontaneously
from the interior of the car to the penny in an illustration of the 2nd Law of thermodynamics.
6. Sort the following process as exothermic or endothermic:
o Endothermic:
o A pair of chemicals are mixed together in a beaker and the beaker becomes cold
o Carbon dioxide converts from a solid to a gas
o Exothermic:
o Your body digests food for energy, generating excess heat
o On a humid day water condenses on a cool surface
o Wood burns in a bonfire
7. When sodium hydroxide is dissolved in water within a beaker, you observe that the beaker becomes
warm. This situation illustrates:
o The 2nd Law of Thermodynamics
o The 1st Law of Thermodynamics
o An Exothermic reaction
8. Select all the following situations that you would classify as endothermic processes:
o Ammonium nitrate dissolves in water and the solution becomes cold
o Lava cools and becomes a solid
o Butane combusts to give a flame in a lighter
o Hand sanitizer evaporating
RADIATION
When we hear the word radiation, often our minds turn to power plants, nuclear weapons, and reactors.
In fact, radiation is so much more and has been part of our universe from the very beginning. In this
lesson, we will explore the concept of radiation and the types of radiation that we encounter.
9. Which of the following are types of electromagnetic radiation?
o X-rays
o Alpha particles
, Week 6 Concepts: Nuclear Chemistry, Energy, and Biochemistry
o Light
o Radio waves
10. Which type of radiation would you consider ionizing radiation?
o Visible light
o Microwaves
o Gamma rays
o Sound waves
11. Which of the following procedures in healthcare involve the use of radiation to take images?
o Temperature measurements using thermometers
o Pulse measurements
o CT scans
o X-Ray
Radiation is a broad term that refers to energy transferred over distance as rays, particles, or waves.
Radiation has always been a part of our world. By the end of this lesson, you should no longer think of all
radiation as dangerous, as there are many forms of radiation with a wide range of properties. The main
categories of radiation we will be focusing on are:
Particulate radiation: Energy transmitted through small particles
Electromagnetic radiation: Energy transmitted through waves or rays without mass
Particulate radiation includes alpha particles as well as electron-based transmission, known as beta
particle radiation. These types of radiation have mass, even if that mass is incredibly small. You will learn
more about the properties of particulate radiation at another time.
Electromagnetic radiation has no mass and includes X-Rays, all forms of light, radio waves, microwaves,
and all other sources of radiation without mass. As you see from the examples, you are always being
exposed to electromagnetic radiation any time there is any degree of light in your presence.
Electromagnetic radiation can also be said to exist as massless particles of energy known as photons and
exist simultaneously as particles and waves.
IONIZING AND NON-IONIZING RADIATION
Another way to categorize radiation is as ionizing or non-ionizing radiation. As you may recall, ions are
charged atoms or molecules.
Ionizing radiation is radiation that is able to cause atoms or molecules to become charged by
removing electrons.
Non-ionizing radiation is NOT able to cause the formation of ions as types of radiation that fall
into this category and cannot remove electrons from atoms or molecules.
The reason that some radiation is ionizing, and others are non-ionizing comes down to energy. High
energy radiation is better able to cause ionization than lower energy forms. This is because it takes
energy to remove electrons.
These categories of radiation overlap with the other categories of radiation: particulate and
electromagnetic. As an example, visible light is a type of electromagnetic radiation that is non-ionizing
while X-Rays are a type of electromagnetic radiation that is ionizing.
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