Unit 2: Elementary Physical, Chemical and Thermodynamic Principles

Question 1

What is a Pure Substance?

Answer 1

A pure substance is a group of elements that has a constant composition and properties that are constant throughout the sample. Either one or multiple elements are chemically bounded.

Question 2

Elements

Answer 2

Are pure substances that cannot be chemically decomposed into simpler atoms. They are represented on the periodic table of elements

Question 3

What are Compounds?

Answer 3

Is a pure substance that is made up of two or more elements that are chemically bound to one another in fixed proportions.

Question 4

Mixtures

Answer 4

Most natural substances in the world are mixtures; that is they are combinations of two or more pure substances that are not chemically bound together. The components of a mixture can therefore be separated by physical means such as screening or distillation.

Question 5

Homogenous Mixtures

Answer 5

A homogeneous mixture is a mixture in which the components that make up the mixture are uniformly distributed throughout the mixture. The composition of the mixture is the same throughout. There is only one phase of matter observed in a homogeneous mixture at a time. So, you wouldn’t observe both a liquid and a gas or a liquid and a solid in a homogeneous mixture.

Homogeneous Mixture Examples
There are several examples of homogeneous mixtures encountered in everyday life:

Air
Sugar water
Rainwater
Vodka
Vinegar
Dishwashing detergent
Steel

Question 6

Heterogeneous Mixture

Answer 6

A heterogeneous mixture is a mixture in which the components of the mixture are not uniform or have localized regions with different properties. Different samples from the mixture are not identical to each other. Heterogeneous mixtures are more common than homogeneous mixtures. There are always two or more phases in a heterogeneous mixture, where you can identify a region with properties that are distinct from those of another region, even if they are the same state of matter (e.g., liquid, solid).

Heterogeneous Mixture Examples

Cereal in milk
Vegetable soup
Pizza
Blood
Gravel
Ice in soda
Salad dressing
Mixed nuts
Bowl of colored candies
Soil

Question 7

Chemical Properties

Answer 7

Chemical Properties are only observed when there is a chemical change or reaction that occurs.

Such as
Heat of Combustion
Toxicity
Flammability

Question 8

Physical Properties

Answer 8

Are those characteristics used to describe a substance or properties that can be observed without a change in the composition of the matter. They include color, hardness, density, the boiling point.

Question 9

Solids

Answer 9

Have an ordered Arrangement of atoms or ions close together, giving them a solid structure with a definite shape and volume. They have very little capability to compress or expand.

Question 10

Liquids

Answer 10

Have a definite volume but no specific shape. Their molecules are close together but are not bound into the rigidity of a solid. They will flow around one another and conform to the shape of their container.

Question 11

Gases

Answer 11

Have no fixed volume or shape because their molecules are in constant motion. They assume the shape of their container. A gas consists mostly of empty space with the gas molecules far apart from one another.

Question 12

Atoms

Answer 12

Atoms are the simplest structures of the world. They are comprised of protons (+), neutrons (Neutral), and Electrons (-).

Question 13

Chemical Reactions

Answer 13

Occurs when elements come together to form new molecules. This means that bonds between elements are broken and new ones are formed. The substances that form due to the chemical reaction are called products. At its core chemical reactions involve the interactions of electrons between different atoms. They do not involve reactions within the nucleus. Instead most occur between electrons in the outer orbital or valance shell. These electrons are either removed, added or shared between two or more different atoms.

Question 14

Evaporation?

Answer 14

Liquid to a Gas

State Change or Physical Change (Change in physical properties without a change in chemical composition.)

Question 15

Condensation

Answer 15

Gas to a Liquid

State Change or Physical Change (Change in physical properties without a change in chemical composition.)

Question 16

Melting

Answer 16

Solid to a Liquid

State Change or Physical Change (Change in physical properties without a change in chemical composition.)

Question 17

Freezing

Answer 17

Liquid to a Solid

State Change or Physical Change (Change in physical properties without a change in chemical composition.)

Question 18

Deposition

Answer 18

Gas to a Solid

State Change or Physical Change (Change in physical properties without a change in chemical composition.)

Question 19

Sublimation

Answer 19

Solid to a Gas

State Change or Physical Change (Change in physical properties without a change in chemical composition.)

Question 20

Can a Liquid be compressed?

Answer 20

Most liquids resist compression, although others can be compressed. … The density of a liquid is usually close to that of a solid, and much higher than in a gas.

Question 21

When are atoms most stable?

Answer 21

Atoms are most stable when the outer shell of electrons is full

Question 22

Chemical Bond

Answer 22

Provides a stable attraction between atoms to form chemical compounds. This is done through the exchange of electrons. As the number of protons and neutrons of each atom does not change through chemical bonding.

Question 23

Covalent Bond

Answer 23

Valence electrons are shared between the atoms creating a new compound. Each atom’s orbital electron shell or valence shell is considered full in covalent bonding.

Question 24

Ionic Bond

Answer 24

Atoms exchange electrons. The atom that loses the electrons becomes a positively charged ion, while the one that gains them becomes a negatively charged ion (anion).

Question 25

Stoichiometry

Answer 25

Stoichiometry is a section of chemistry that involves using relationships between reactants and/or products in a chemical reaction to determine desired quantitative data. In Greek, stoikhein means element and metron means measure, so stoichiometry literally translated means the measure of elements.

Question 26

Thermodynamics

Answer 26

Thermodynamics is the branch of physics that deals with the relationships between heat, work and other forms of energy. In particular, it describes how thermal energy is converted to and from other forms of energy and how it affects matter. Such as the conversion of energy from fossil fuels into mechanical work.

Question 27

Heat

Answer 27

Heat is energy transferred between substances or systems due to a temperature difference between them, according to Energy Education. As a form of energy, heat is conserved, i.e., it cannot be created or destroyed. It can, however, be transferred from one place to another. Heat can also be converted to and from other forms of energy. For example, a steam turbine can convert heat to kinetic energy to run a generator that converts kinetic energy to electrical energy.

Question 28

Temperature

Answer 28

Temperature is simply the measure of the speed at which a body’s molecules vibrate. The amount of heat transferred by a substance depends on the speed and number of atoms or molecules in motion, according to Energy Education. The faster the atoms or molecules move, the higher the temperature, and the more atoms or molecules that are in motion, the greater the quantity of heat they transfer.

Question 29

Heat transfer

Answer 29

Heat can be transferred from one body to another or between a body and the environment by three different means: conduction, convection and radiation.

Question 30

The First Law of Thermodynamics

Answer 30

states that energy can neither be created nor destroyed; energy can only be transferred or changed from one form to another. For example, turning on a light would seem to produce energy; however, it is electrical energy that is converted.

Question 31

The Second Law of Thermodynamics

Answer 31

The second law of thermodynamics says that the entropy of any isolated system always increases. Isolated systems spontaneously evolve towards thermal equilibrium—the state of maximum entropy of the system. Essentially heat energy generated cannot be completely converted to work, due to small losses of heat energy in a given system or plant.

Question 32

Entropy

Answer 32

The entropy of an object is a measure of the amount of energy which is unavailable to do work. Entropy is also a measure of the number of possible arrangements the atoms in a system can have. In this sense, entropy is a measure of uncertainty or randomness.

Question 33

Thermal Expansion

Answer 33

Represents the expansion and contraction of solids as they undergo a temperature increase or decrease.

Question 34

Coefficient of Linear Expansion

Answer 34

The change in length of a solid per unit length, per degree rise in temperature. Linear Dimensions include length, width, height, or anything that changes its dimensions.

Question 35

Linear Expansion

Answer 35

The increase in linear dimension due to heating.

Question 36

Litres to Kilograms?

Answer 36

They are equivalent units of conversion 1L = 1Kg

Question 37

Thermal Shock

Answer 37

Thermal shock is a variation in temperature which causes tension in a material. It frequently causes breakage in the material, and is most common in brittle materials such as ceramics. This is a process that takes place abruptly when there is a sudden variation of temperature.

Question 38

FBC

Answer 38

Fluidized Bed Combution Steam Generators burn solid fuels. These steam generating units uses the combustion gas to suspend the solid fuels in the furnace in a bed of inert material like limestone. Though this burning bed is comprised of solid it behaves more like a suspended fluid.

Question 39

Advantages of Electric Boilers?

Answer 39

Compact 
No fuel storage
Produce no pollution
Silent in operation
No threat of explosion

Question 40

Baretube Heat Exchanger

Answer 40

Most common tube used in boilers and are easy to clean. Less likely to experience fouling (blockage of piping with solid material or covering of piping with solid materials)

Question 41

Finned Tube Heat Exchangers

Answer 41

Provides a large area for heat transfer but is prone to fouling and must be kept in a clean and frost free enviroment.

Question 42

Two-phase heat transfer fluid

Answer 42

Steam