CHEMISTRY ATI TEAS SCIENCE CHEMISTRY Questions related to chemistry - - PDF document
ATI TEAS SCIENCE REVIEW CHEMISTRY ATI TEAS SCIENCE CHEMISTRY Questions related to chemistry test your knowledge of chemical properties and processes. You may be asked questions about states of matter, properties of matter, phase changes,
Questions related to chemistry test your knowledge of chemical properties and processes. You may be asked questions about states of matter, properties of matter, phase changes, chemical bonds, chemical solutions, chemical reactions, and acids and bases. You may be asked to balance chemical equations. Let’s get started in understanding how chemistry is important on the ATI TEAS.
UNDERSTANDING STATES OF MATTER Matter is made up of microscopic particles that move different speeds depending on the energy they are exposed to. We measure this energy as temperature. The molecules can move either quickly and randomly
When the energy is high, matter take the form of a gas, in which molecules are moving about quickly and are far apart. Gases have no fixed form. Molecules are free to move at random past each other, and they tend to fill any container that holds them. If a gas is not contained, its molecules will disperse.
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UNDERSTANDING STATES OF MATTER Lower temperatures result in a liquid, in which molecules cohere but are fluid. Coherence means that the molecules remain close together, but they can change position by sliding over one another. In liquids, molecules move less freely than in a gaseous state, sliding past one
portion of a container. When the temperature is low, matter takes the form of a solid, in which molecules are packed closely together and retain their positions. Solid matter is rigid, and molecules retain a uniform spacing. A solid has a defined form, which is brittle. It can be broken into pieces but tends to stay together. A somewhat unusual state of matter is plasma, which is like a gas in many of its properties but carries an electric charge. The TEAS focus on solids, liquids, and gases.
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UNDERSTANDING CHANGES IN STATE OF MATTER The state of matter depends on temperature and pressure. Higher temperatures cause molecules to energize and move farther apart. Increasing pressure forces molecules closer together. Melting is the phase change from solid to liquid and boiling is the phase change from liquid to gas. There is also a direct change from solid to gas known as
the change from liquid to solid is freezing. A direct change from gas to solid is deposition.
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UNDERSTANDING PROPERTIES OF MATTER All types of matter can be described in terms of the physical and chemical properties each substance has. Physical properties are observable and there is an extensive list of physical properties that one could observe about a substance. A few examples are density, the temperatures at which the substance undergoes phase changes, malleability, conductivity, specific heat capacity, mass, volume, color, and many other properties. Physical properties are further divided into intensive and extensive properties. An intensive property does not depend on the size or amount of matter in the
amount of matter in the object. For example, mass is extensive because the measurement would change the size of the sample. Boiling point is intensive because the temperature at which the object boils is not dependent on its volume.
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UNDERSTANDING PROPERTIES OF MATTER Water is a polar inorganic compound that is transparent and nearly colorless. H2O is a covalent compound because oxygen and hydrogen are nonmetals. It has 8 total valence electrons (6 from oxygen and 1 from each hydrogen). Breaking the bonds requires a lot of energy, so water has a very high specific heat and heat of vaporization. The molar mass of water is 18.02 g/mol. It commonly exists as solid, liquid, and gas.
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UNDERSTANDING PROPERTIES OF MATTER The polarity of water allows it to exhibit both cohesive and adhesive properties. Cohesiveness allows water to travel through tiny capillaries and creates surface tension on the surface of a body of water. Adhesiveness allows water to stick to other molecules and dissolve them, making it known as the “universal solvent.”
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UNDERSTANDING PROPERTIES OF MATTER Water also has a unique property called osmosis, which is a specific type of diffusion. Diffusion is a term used to describe the process of a substance moving from an area of high concentration to an area of low concentration. Osmosis is a type of diffusion in which water moves passively through a semi-permeable membrane to equalize water concentration
through cell walls in the body.
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UNDERSTANDING CHEMICAL BONDS A chemical compound is created when two or more atoms join to form a chemical bond that leaves the atoms in a less excited state than they were in before the bond. Such bonds form in two ways.
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UNDERSTANDING CHEMICAL BONDS A covalent bond occurs when atoms share electrons between them. This type of bond is common between two atoms of the same element, as in hydrogen (H2) or in similar
covalent bond. Alkanes, for example, share a single bond. In some compounds, one atom takes the shared electron for more time, due to its structure, forming a polar covalent
molecules form a double bond, sharing four electrons as opposed to two. These bonds are commonly represented in the alkenes, hydrocarbons with twice as many hydrogen molecules as carbon molecules. It is possible to form triple bonds as seen in a group of hydrocarbons called alkynes.
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UNDERSTANDING CHEMICAL BONDS An ionic bond is created between atoms when one atom gives an electron to the other. These bonds typically take place between metals and nonmetals due to the unique electron configuration of metals, with the metal giving an electron to the nonmetal. This transfer creates a positive charge and a negative charge at the ends of the compound. The positive charge, or cation, is created by the giver of an electron. The negative charge,
compounds remains balanced at zero.
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UNDERSTANDING CHEMICAL SOLUTIONS A chemical solution is a group of chemical compounds evenly distributed in a state of
completely dissolved in the others. This is most easily achieved in a liquid state. There are mixtures that are not solutions. A heterogeneous mixture maintains separation between two substances, like oil and water.
UNDERSTANDING CHEMICAL SOLUTIONS The solute is the compound dissolved in the solvent. Liquids make excellent solvents. The solubility of a solvent depends on the nature of the liquid as well as external factors like temperature. The concentration of the solution is the amount of solute in the
compound’s molecular mass.
UNDERSTANDING CHEMICAL REACTIONS To create a new chemical compound from other elements and compounds, a chemical reaction is needed. Two or more reactants are added together, often with an input of energy, creating one or more products and by-products. Photosynthesis occurs, for instance, when a plant cell combines carbon dioxide and water. The sun’s rays provide the energy. The chemical reaction produces sugar and oxygen. Chemical reactions are shown with equations and have a basic pattern: reactants go on the left and products go on the right, with the reaction sign (an arrow) showing the direction of the reaction in the
the middle. Here is an example showing the formation of water molecules: 2"# + %# → 2"#% Equations for chemical reactions must be balanced; there must be the same number of atoms of each element on both sides of the reaction. Notice in the equation above that there are four hydrogen atoms and two oxygen atoms on each side. Only their arrangement is changed.
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UNDERSTANDING CHEMICAL REACTIONS There are five basic types of chemical reactions:
compound
compounds
another element or compound in a compound
iconic compounds
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UNDERSTANDING CHEMICAL REACTIONS Reaction rates depend on the likelihood of collision between particles. The reaction rate can be altered by changing the following factors:
collisions.
collisions are likely and will have more energy.
are more likely
bigger the surface, the faster the reaction. Breaking up a sample into smaller particles provides more surface area for collisions.
reaction but is chemically unchanged at the end of the reaction.
UNDERSTANDING CHEMICAL REACTIONS Chemical reactions occur in nature and in the laboratory. A catalyst will speed up the reaction by lowering the amount of energy needed to start the reaction. Enzymes act as catalysts in cellular processes. They quicken the chemical reaction, turning a molecule, known as a substrate, into a product without being altered themselves.
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UNDERSTANDING ACID BASE BALANCE Many acids and bases can be understood from the perspective of the theory developed by Arrhenius, a Swedish scientist. In this view, an acid is a substance that gives off hydrogen (H+) ions when it is dissolved in water. A base, or alkaline substance, is a substance that gives off hydroxide (OH-) ions when it is dissolved in water. Acidic solutions have higher concentrations of hydrogen ions, whereas alkaline solutions have lower concentrations of hydrogen ions. The presence of acids and bases can be tested using tools known as
turns red in the presence of a base.
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UNDERSTANDING ACID BASE BALANCE Here are some examples of acids and their chemical formulas. ACID CHEMICAL FORMULA
!"#!$%#
!$&%'
!$"(!)%*
HCL
!#+%'
BASE CHEMICAL FORMULA
LiOH
KOH
NaOH
IMPORTANT NOTE: ACID = ACID; BASE = HYDROXIDE
UNDERSTANDING ACID BASE BALANCE The acidity or alkalinity of a solution is measured using a scale known as the pH scale. \ Each step of the pH scale has 10 times the difference in concentration
a pH of 7 will have 10 times more hydrogen ions than a solution with a pH of 8 and 10 times fewer hydrogen ions than a solution with a pH of 6.
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UNDERSTANDING BALANCING CHEMICAL EQUATIONS The TEAS Science section may contain questions that ask you to balance chemical equations. We will outline the steps in this process later in this review. One of the most important chemical equations for humans is the one that represents photosynthesis. Without the following equation, there would be no life on Earth: !"# + %#" ⟹ !'%(#"' + "# This equation shows how green plant cells, with the help of the sun’s energy, convert carbon dioxide (!"#) and water (%#") into glucose and
left side of the arrow. The arrow shows the direction of production. The two products, sugar and oxygen, are on the right side of the arrow.
UNDERSTANDING BALANCING CHEMICAL EQUATIONS According to the Law of the Conversation of Mass, in a chemical reaction, no energy is lost, but neither is mass destroyed. The amount
those products escape as a gas or a liquid. In the photosynthesis equation, there is a difference in the number of atoms on the right and left sides:
Element Reactants Products C 1 6 H 2 12 O 3 8
To produce sugar and oxygen requires more reactants than we have
UNDERSTANDING BALANCING CHEMICAL EQUATIONS We can multiply any molecule with a number, called a coefficient. We cannot change the subscript, however, without changing the nature of the molecule. By adding coefficients to the reactants and products, we can balance the equation in a few simple steps. The best way to do this is by balancing each element in turn. Start with the carbon. The right side has 6 carbon atoms, so the left side needs 6: !"#$ + &$# ⟹ "(&)$#( + #$
UNDERSTANDING BALANCING CHEMICAL EQUATIONS !"#$ + &$# ⟹ "(&)$#( + #$ Here we have multiplied the "#$ by 6 to result in 6 carbon atoms on the left side. When we multiply "#$ by 6, this also change the number
total of 13. The 2 changed numbers are shown underlined in the following table.
Element Reactants Products C 6 6 H 2 12 O 13 8
Now the carbon is equal, but the hydrogen remains unequal, and the
UNDERSTANDING BALANCING CHEMICAL EQUATIONS Next, we fix the hydrogen: !"#$ + !&$# ⟹ "(&)$#( + #$ Here we multiplied the &$# molecule by 6 to result in 12 hydrogen 2 atoms on the left side. When we multiple &$# by 6, the further changes the 2 number of the oxygen atoms on the left side from 13 to
&$# molecule, for a total of 18.
Element Reactants Products C 6 6 H 12 12 O 18 8
UNDERSTANDING BALANCING CHEMICAL EQUATIONS The last remaining imbalance rests with the oxygen. At this point, there is plenty of oxygen in the reactants. We can balance the equation by producing more !". #$!" + #&"! $'&("!' + #!" In this step, the !" molecule on the right side was multiplied by 6. This resulted in 18 oxygen atoms on the right side. The equation is now
right sides.
Element Reactants Products C 6 6 H 12 12 O 18 18