- a reaction occurs with no outside force
This chem talk is about Thermodynamics. Thermodynamics is the study of how heat and other forms of energy are involved in chemical and physical reactions, and kinetics is the study of reaction rates and how they can be affected by variables such as concentration, particle size, and temperature. In this section, it talks about different types of reactions. A chemical reaction that continues to occur pm its own once it begins is called a spontaneous reaction. An enthalpy change is a change in heat energy that occurs ar constant pressure. Energy diagrams are graphs that show how energy changes during the course of reactions. To tell if the overall enthalpy change is endothermic or exothermic is by the relative locations of the reactant energy and product energy. Bonds must always be broken in the reactants before new bonds can form in the products. Activation energy is the energy that must be gained by molecules so they can break existing bonds and undergo a reaction. Activated complex is the intermediate state that is a combination of reactant and product atoms. Lastly, a catalyst is a substance that provides a lower energy pathway for a reaction which increases the speed of a reaction.
This chem talk is about chemical structures and isomers. Isomers are compounds that have the same chemical formulas but different structural formulas. A hydrocarbon with no double or triple bonds is a saturated carbon. An unsaturated carbon is a hydrocarbon with one or more double or triple bonds. We have spent a lot of time in class with Lewis Structures, which is a system of showing chemical structures in which the valence electrons of an atom are placed around the atom. We’ve also talked a lot about polar covalent bonds. They are bonds between two atoms of different electronegativity. I have not heard very much about cis and trans structures. Cis- double bond is a geometric arrangement of a carbon to carbon double bond where the hydrogen atoms are located on the same side of the double bond. Trans- double bonds are a geometric arrangement of a carbon to carbon double bond where the hydrogen atoms are located on opposite sides of the double bond. We have focused on tetrahedrons in class. They are a pyramid with four sides that are equilateral triangles in geometry, but in chemistry, it is a term used for molecular structures in which there are four bonds at equal angles between each other around an atom. Lastly, the word micelle I have never heard of. It is an aggregation of molecules that have a polar end and a non-polar end such that in aqueous solution, the polar ends will lie outside the aggregate attracted to water, and the nonpolar ends will be inside the aggregate, away from the water.
- NaCl conducts electricity because when the crystals dissolve in water the sodium ions and chloride ions separate from the crystal.
- An electrolyte is a substance that dissolves in water to make solutions that conduct electricity and non-electrolytes are molecules that do not form ions in a solution.
- The Zinc electrons come from the zinc metal and then travels through the wire. Then the electrons reach the copper and the copper takes them. Reduction then takes place.
- The anode of a battery is when oxidation takes place and the electrons are released into the circuit. The anode is negative when giving away. It is where the electrons are released.
- The cathode of the battery is where reduction takes place and the electrons are received. The cathode is positive when receiving. It is at the end where the electrons are received.
This Chem Talk was about solutions that conduct electricity. A solute that forms ions in an aqueous solution is an electrolyte. A nonelectrolyte is a solute that does not form ions in solution and can not conduct an electric current. An ion is an atom or molecule that has acquired a charge by either gaining or losing ions. I did not know that in the path of electricity in a battery has a half cell which has an anode and a cathode. A half cell is in electrochemical batteries, each of two cells that contain an electrode surrounded by a solution. Two half cells are connected by a salt bridge. In class, we used a salt bridge. A salt bridge is a lab device used to connect the oxidation and reduction half cells of an electrochemical cell. It allows excess negative ions to pass from cathode to the anode. An anode is the negative battery electrode that removes electrons in an electrical circuit. In an electrochemical cell, oxidation takes place at the anode terminal. A cathode is the positive battery electrode that receives electrons in an electrical circuit. Reduction takes place at the cathode terminal in an electrochemical cell.
This Chem Talk was about Redox Reactions and metals. Metals are a class of materials that exhibit the properties of conductivity, malleability, reactivity, and ductility. Metallic elements lose electrons, so they form positive ions in ionic compounds. We were also introduced to the Activity Series which is a chart of metals listed in order of declining relative reactivity. Oxidation-reduction, also known as redox is a chemical reaction in which electrons are transferred from one substance to another. Oxidation is a loss of one or more electrons and reduction is a gain of one or more electrons.
This Chem Talk is about Stoichiometry, which is the relationship between the relative quantities of substances taking part in a reaction or forming a compound, typically a ratio of whole integers. I have never heard this word before, but I have heard of moles and molar mass. A mole is the number equal to the number of carbon atoms in exactly 12 grams of pure^12C. The mass of one mole of a pure substance is molar mass. Also, this Chem Talk informs the reader about balancing chemical equations. The standard temperature and pressure is the standard temperature, which is 273.15 kelvins and standard pressure, which is 760 mm Hg. Dimensional analysis is a name for “equivalent measures.” A method for solving problems that involve canceling units. Percent yield is the ratio of the product recovered to the product expected expressed as a percent.
This chem talk was about the Law of Conservation of Matter. The amount of matter present before and after a chemical change remains the same is the Law of Conservation of Matter. Matter cannot be destroyed, but it can change form.
This chem talk talked about intermolecular forces vs. kinetic molecular motion. Intermolecular forces are the attractive forces acting between molecules. For example, the force between molecules in a solid consist of vibrating in place, which makes the solid have a definite shape and the force between molecules in a gas are not vibrating in place, but moving around, not making it have a definite shape. Nonpolar molecules are molecules that have small intermolecular forces due to the symmetry of charge distribution. Examples of these are halogens, oxygen, nitrogen, carbon, dioxide, and the CX4 molecules. As the size of nonpolar molecules increases, the attractive forces between molecules also increase. London dispersion forces are weak intermolecular forces that cause the electrons of an atom or a molecule to shift slightly to form a temporary dipole moment. They are difficult to separate. Electronegativity is the ability of an atom of an element to attract electrons in a chemical bond. Oxygen is more electronegative than hydrogen. The O-H bonds are pulled closer to the oxygen atom. A polar bond is the difference in the electronegativity of neighboring atoms causes the electrons to be attracted more to one of the atoms of the bond, making one atom slightly negative and the other slightly positive. Hydrogen bonds are the intermolecular attraction of a polarized hydrogen atom to nearby highly electronegative atom, such as oxygen, nitrogen, or fluorine. Lastly, van der Waals forces are weak intermolecular attraction forces between molecules.
In this Chem Talk, it talked about paints and precipitates. Along with talking about paints, it also introduced to the reader what color pigments were. This Chem Talk first talked about “using solid precipitates as pigments”. In the lab we had just completed, we created solid precipitate called insoluble compounds, which can be used to create color in paint. In the lab, we used aqueous solutions. Prior to combining the cations, an ion that has a positive charge, and an anion, an ion that has a negative charge, together, they were in separate aqueous solutions, and when were mixed, they created a precipitate. A precipitate is an insoluble salt that is formed when two solutions are mixed together. A compound that is composed of cations and anions is an ionic compound form because of the strong attraction, and then they get removed from the water solution. A double-replacement is a reaction in which two ions in the two different compounds exchange places to form new compounds. Spectator ions are ions that do not participate in the reaction and remain in solution before and after the reaction. A chemical equation for a reaction that lists only those compounds participating in the reaction. After we completed the lab, we composed equations for each reaction that formed participates. We made an equation that was just included words, one with the chemical symbols and charges, and lastly an ionic equation. A substance that dissolves in a liquid is soluble and one that doesn’t is insoluble.