5/17/17 – Hwk

Checking Up 1-7 p.349

  1. When a change occurs spontaneously is a reaction that continues own its own without input energy once it has started.
  2. The two questions that must be answered are can a reaction occur spontaneously and how fast can the reaction occur.
  3. When determining whether a change is exothermic or endothermic one must look at the energy input and output. In exothermic there is an input of energy and it is the opposite for endothermic. 
  4. The energy in a exothermic reaction comes from the forming of bonds.
  5. The engineers added magnesium and water to increase the speed of the reaction.
  6. The catalyst provides a lower-energy pathway so that starting materials have enough energy to get over the energy barrier.
  7. The graph with a catalyst starts on a higher energy level than the graphs without a catalyst. However, both types of graphs have similar trendlines once activated complex is reached.

Chem Talk: Thermodynamics

The chem talk on thermodynamics focuses on heat changes. Thermodynamics is the study of how heat and other forms of energy are involved in chemical and physical reactions. Thermodynamics is useful in determining whether or not a reaction can occur spontaneously. In relation to thermodynamics, kinetics is the study of reaction rates and how they can be affected by variables such as concentration, particle, size, and temperature. Similar to thermodynamics, kinetics can determine how fast a reaction can occur. 

In the lab heat energy was released when the system went from a higher energy to a low energy. Meaning the cause of this must either be endothermic or exothermic reaction.

When a chemical reaction happens the bonds in the reactants break and new bonds are formed creating products. In order to break bonds energy is needed so it is an endothermic change. However, when energy is released bonds must be being formed so it is an exothermic change.

The overall change can be caused by either the reactions but it depends on whether the total energy input or total energy output is greater.

Understanding thermodynamics is fairly simple because it is a matter of finding out what energy input or output is greater to determine what kind of reaction has occurred.

5/10/17 – Hwk

p.338 Checking Up Q. 1-5

  1. Solutions containing salt can conduct electricity because it is able to form ions however solutions that contain sugar cannot conduct electricity since they are unable to form ions.
  2. Electrolytes are able to form ions and a non-electrolyte does not form ions.
  3. The electrons in the battery come from the metal electrodes used in the half reactions. Then from there the Zn -> Zn^2+ and Cu^2+ goes to Cu.
  4. The anode of the battery is the negative electrode and where the electrons are removed (oxidation).
  5. The cathode of the battery is the positive electrode and where the electrons are received (reduction).

Chem Talk: Solutions that Conduct Electricity

The next lab that we are going to do in class is going to involve investigating what solutions conduct electricity. Electrolytes are the substances that dissolve in water that enable it to conduct electricity. In order for this to happen a solution must have charged particles and these charged particles must be able to move around. When a compound dissolves in water and creates charged particles it is called an ion. An ion is an atom or molecule that has acquired a charge by either gaining or losing electrons.  These compounds most commonly have positively charged metal ions and a negatively charged ion to balance out the charge. Solutions that are made of molecules dissolved in water to not conduct electricity. These solutions are called non-electrolytes because they do not form ions therefore cannot conduct electricity.

A battery is composed of two half cells. Each of these two cells contain electrodes that are surrounded by a solution. These two half cells are then connected by a salt bridge. A salt bridge is a lab device that connects the oxidation and reduction half cells of an electrochemical cell. Its purpose is to allow excess negative ions to pass from the cathode to the anode.

It make sense that the half cells depend on one another. When oxidation is occurring a reduction reaction is also simultaneously happening.

Chem Talk: Redox Reactions

Talking about metals is nothing new to us in class and it is not a shock when it comes up in the textbook. Metal is a material that consists of conductive, malleable, reactive and ductile features. Hence why they are often used in cookware and electrical wiring. Metals can withstand high levels of heat and are capable of being formed into different shapes while maintaining their strength. Metals are most commonly found in nature in their ionic forms which are positively charged ions that are in solid crystals or dissolved in water. Another important feature to know about metals is that metallic elements lose electrons more easily than non-metallic elements, therefore forming positive ions in ionic compounds. 

Oxidation-reduction or redox reactions occur when electrons are transferred from one substance to another. Oxidation is defined as a loss of one or more electrons and reduction is a gain of one or more electrons. So when oxidation and reduction changes occur at the same time it is called a half-reaction because both halves are needed in order for the reaction to happen. Half-reactions can be used to balance redox equations by making sure the number of electrons lost is equal to the number of electrons gained. 

Chem Talk: Stoichiometry

The Chapter 4 Section 3 Chem Talk on Stoichiometry mentioned material that we have covered before in class but it also introduced some new information that allows us to go deeper into topics we have already done in class.  The Chem Talk began with a review on moles and molar mass. A mole is used to count large quantities of small objects. More specifically the number equal to the number of carbon atoms in 12 grams of pure carbon. The important take away from all this is that one mole of anything is always the same quantity. Furthermore, one mole of any single kind of atom or molecule has a mass equal to its atomic or molecular mass in grams. An example of this is an oxygen atom has an atomic mass of 16.00amu meaning that one mole of oxygen atoms has a mass of 16.00g. This number is the molar mass of the oxygen atoms.

In the upcoming class we will be investigating the volume of carbon dioxide gas needed to fill up a balloon. We will achieve this by calculating the number of moles the reactants needed. This entire process is called stoichiometry. Stoichiometry is the study of the relationships among substances involved in chemical reactions.

Chem Talk: Law of Conservation of Matter

Balanced chemical equations are an example of the law of conservation of matter. Matter cannot be created or destroyed but are able to change form. The law of conservation is the amount of matter present before and after a chemical change stays the same. Even though the same amount of each element must enter and exit with the same amount. Elements can be partnered with different elements on each side. This means that in a chemical equation the amount of an element on the reactant side must equal that on the product side. However, the atoms of the elements can be bonded differently.

Recently in class we have been talking about intermolecular forces more specifically the kinds of bonds that make up those forces. Learning about the different kinds of intermolecular forces is very interesting since there is so many kinds of bonds with varying strengths and energy levels. The stronger the intermolecular force the higher the boiling point the weaker it is the lower the boiling point is. The strongest of the bonds is ion-ion with an energy of 800 and London dispersion forces with the lowest energy of 10.

4/14/17 – Hwk

Checking Up Questions

  1. A molecule’s polarity is related to the attraction between molecules. The attraction between each molecule is dependent upon what state of matter it is in.
  2. London dispersion forces by definition are attractive forces that are much weaker than ionic or covalent bonds which hold atoms together.
  3. C^7H^16

Chem to Go 

4. C

Chem Talk: Intermolecular Forces vs. Kinetic Molecular Motion

This weeks Chem Talk on intermolecular forces in states of matter covered material that we have studied in class before but went into a bit more detail. Intermolecular forces refers to the attractive forces acting between molecules this in turn dictates the number and position of electrons. The particles within a solid have restricted movement since there is a strong attraction between molecules. Solids movement consists of vibrating which gives solids a definite volume and shape. When a solid is heated up vibrations become so energetic that particles begin to break free creating a liquid.

Then while in a liquid state the particles are free to move around because they are not in a fixed position yet still have a definite volume but no definite shape. If the liquid is heated up to the point where the kinetic energy makes the attraction between the molecules loosen then the substance becomes a gas. Once a gas state is reached the distance between the atom is no longer restricted and there is no definite shape or definite volume.

Nonpolar molecules are molecules that have shapes and bonds that are symmetrical. The electrons within these molecules are spread out in a way that there are no permanent electrical charges and the intermolecular forces between the molecules is small. 

The chem talk was helpful review and the new material was a good addition to my foundation of intermolecular forces.

Chem Talk: Chemical Structures

Recently in class we have been going over material that we have seen before and worked with on multiple occasions. Earlier this year we were introduced to some fundamental aspects of chemistry such as lewis dot structures and covalent bonds. A lewis dot structure is a diagram that displays the outer-shell valence electrons. More specifically a system that shows the chemical structure in which the valence electrons of an atom are placed around the atom. Bonds are shown as a pair of dots or a solid line. Non-bonding valence electrons are shown as dots on the outskirts of the elements in the compound. When finding out the number of electrons in each bond one must find the row and type of metal on the periodic table. Each atom must have eight electrons in order for it to be balanced. The electrons that are paired are the valence electrons and the atoms by themselves are lone pairs. I really enjoy making lewis dot structures because it is not only fun but very informative and useful. It makes it easier to understand compounds and what components form their characteristics.