Unit 2: Elementary Physical, Chemical and Thermodynamic Principles Flashcards
What is a Pure Substance?
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.
Elements
Are pure substances that cannot be chemically decomposed into simpler atoms. They are represented on the periodic table of elements
What are Compounds?
Is a pure substance that is made up of two or more elements that are chemically bound to one another in fixed proportions.
Mixtures
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.
Homogenous Mixtures
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
Heterogeneous Mixture
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
Chemical Properties
Chemical Properties are only observed when there is a chemical change or reaction that occurs.
Such as
Heat of Combustion
Toxicity
Flammability
Physical Properties
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.
Solids
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.
Liquids
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.
Gases
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.
Atoms
Atoms are the simplest structures of the world. They are comprised of protons (+), neutrons (Neutral), and Electrons (-).
Chemical Reactions
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.
Evaporation?
Liquid to a Gas
State Change or Physical Change (Change in physical properties without a change in chemical composition.)
Condensation
Gas to a Liquid
State Change or Physical Change (Change in physical properties without a change in chemical composition.)
Melting
Solid to a Liquid
State Change or Physical Change (Change in physical properties without a change in chemical composition.)
Freezing
Liquid to a Solid
State Change or Physical Change (Change in physical properties without a change in chemical composition.)
Deposition
Gas to a Solid
State Change or Physical Change (Change in physical properties without a change in chemical composition.)
Sublimation
Solid to a Gas
State Change or Physical Change (Change in physical properties without a change in chemical composition.)
Can a Liquid be compressed?
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.
When are atoms most stable?
Atoms are most stable when the outer shell of electrons is full
Chemical Bond
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.
Covalent Bond
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.
Ionic Bond
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).
Stoichiometry
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.
Thermodynamics
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.
Heat
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.
Temperature
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.
Heat transfer
Heat can be transferred from one body to another or between a body and the environment by three different means: conduction, convection and radiation.
The First Law of Thermodynamics
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.
The Second Law of Thermodynamics
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.
Entropy
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.
Thermal Expansion
Represents the expansion and contraction of solids as they undergo a temperature increase or decrease.
Coefficient of Linear Expansion
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.
Linear Expansion
The increase in linear dimension due to heating.
Litres to Kilograms?
They are equivalent units of conversion 1L = 1Kg
Thermal Shock
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.
FBC
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.
Advantages of Electric Boilers?
Compact No fuel storage Produce no pollution Silent in operation No threat of explosion
Baretube Heat Exchanger
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)
Finned Tube Heat Exchangers
Provides a large area for heat transfer but is prone to fouling and must be kept in a clean and frost free enviroment.
Two-phase heat transfer fluid
Steam
