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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, 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. COVERED AREAS Understanding States of Matter. Understanding Changes in States of Matter. Understanding Properties of Matter Understanding Chemical Bonds. Understanding Chemical Solutions. Understanding Chemical Reactions. Understanding Acid Base Balance. Understanding Balancing Chemical Equations. 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 or hardly at all. 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.
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 another. They have a fixed volume but will flow freely unless they fill a 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. 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 sublimation. The phase change from gas to liquid is condensation and the change from liquid to solid is freezing. A direct change from gas to solid is deposition. 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
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. 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 elements. When a molecule shares a pair of electrons in a stable state, it has formed a 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 bond. This molecule is partly negatively charged and partly positively charged. Some 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. 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, or anion, is located at the receiving end of the electron. The net charge of the compounds remains balanced at zero. UNDERSTANDING CHEMICAL SOLUTIONS A chemical solution is a group of chemical compounds evenly distributed in a state of matter. The solution is a homogenous mixture where one chemical compound is 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. 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 solution. The mole is the unit of measurement for chemical reactions and refers to a compound’s molecular mass.
For example: A + BC ⟹AC + B
- Double replacement : 2 ionic compounds create two more iconic compounds For example: AB + CD ⟹AD + CB Reaction rates depend on the likelihood of collision between particles. The reaction rate can be altered by changing the following factors:
- Concentration – The more particles there are, the higher the chance of collisions.
- Temperature – Particles excite at higher temperatures, so more collisions are likely and will have more energy.
- Pressure – Increased pressure forces particles together, so collisions are more likely
- Surface area – In a solid, only particles at the surface can collide. The bigger the surface, the faster the reaction. Breaking up a sample into smaller particles provides more surface area for collisions.
- Catalysts – A catalyst is a substance that changes the rate of a chemical reaction but is chemically unchanged at the end of the reaction. 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. 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 indicators. One indicator in common use litmus paper. Litmus paper turns red in the presence of a base. Here are some examples of acids and their chemical formulas. ACID CHEMICAL FORMULA
- Acetic Acid HC 2 H 3 O 2
- Phosphoric Acid H 3 PO 4
- Citric Acid H 3 C 6 H 5 O 7
- Hydrochloric Acid HCL
- Sulfuric Acid H 2 SO 4 BASE CHEMICAL FORMULA
- Ammonium Hydroxide NH 4 OH
- Lithium Hydroxide LiOH
- Magnesium Hydroxide Mg (OH) (^2)
- Potassium Hydroxide KOH
- Sodium Hydroxide NaOH IMPORTANT NOTE: ACID = ACID; BASE = HYDROXIDE The acidity or alkalinity of a solution is measured using a scale known as the pH scale.
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: CO 2 + H 2 O C 6 H 12 O 6 + O 2 This equation shows how green plant cells, with the help of the sun’s energy, convert carbon dioxide (CO 2 ) and water (H 2 O) into glucose and oxygen (O 2 ). The two reactants, carbon dioxide and water, are on the 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. According to the Law of the Conversation of Mass, in a chemical reaction, no energy is lost, but neither is mass destroyed. The amount of reactant must match the amount of products that are made, even if 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 on the left side. The solution is to balance the two sides. ATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI
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: 6 CO 2 + H 2 O C 6 H 12 O 6 + O 2 6CO 2 + H 2 O C 6 H 12 O 6 + O 2 Here we have multiplied the CO 2 by 6 to result in 6 carbon atoms on the left side. When we multiply CO 2 by 6, this also change the number of oxygen atoms on the left side from 3 to 13. There are now 12 oxygen atoms in the CO 2 molecule, plus 1 in the H 2 O molecule, for a 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 oxygen has changed in number. Next, we fix the hydrogen: ATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI
In this step, the O 2 molecule on the right side was multiplied by 6. This resulted in 18 oxygen atoms on the right side. The equation is now balanced. Each element has the same number of atoms on the left and right sides. Element Reactants Products C 6 6 H 12 12 O 18 1 ATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI TEAS SCIENCE REVIEW- CHEMISTRYATI
