Last Chem Talk

Alright guys this ones a long one, so kick back with a bowl of popcorn while I teach you all about energy and the many other things that go along with that. Our lab today put our theories to test as we observed how the rubber band released and absorbed energy. When talking about change, chemists refer to the system and the surroundings. Basically, the system i the reaction and everything that is under study. The surroundings on the other hand are everything in the universe that are not under study. We raise many questions to help us understand what is going on in the system. For example, “is the rubber band producing or absorbing heat?” Also, there are different types of systems. First, there is the open system. This is where energy can pass between the system and the surroundings. Secondly and lastly, there is the closed system. This is a system that is isolated from the surroundings and heat cannot enter nor leave. Im sure it won’t be hard for you to remember which one is which. Now, lets focus in on understanding energy or enthalpy. When heat energy is releases from a system, this is known as a exothermic change. While the system releases energy, its surroundings gain energy. You see this when something feels warm such as a fire. So, this all means that the enthalpy of the reaction is negative. When the heat energy is absorbed from the system, this is known as an endothermic change. While the system absorbs energy, the surroundings give off the energy. So, all of this means that the enthalpy of the reaction is positive. The energy can never just disappear and we know this from the law of conservation of energy. When a reaction occurs the particles also change and they move around in the system. The change in disorder is called entropy. As particles get more disordered the entropy increases. This makes the entropy positive. As particles get less disordered the entropy decreases. This makes the entropy negative. Gas to Solid would be an example of less disorder. Okay, i hope everyone is still awake because were gonna put our knowledeg delta H (enthalpy) and delta S (entropy) together to predict spontaneity in nature! In short, reactions can occur and they also cant occur. The relationship between all of these is delta H – temperature X delta S. It is spontaneous if the equation produces a negative. If delta H is negative and delta S is positive then the reaction will be with out a doubt spontaneous. If delta H is positive and delta S is negative then the reaction will be non spontaneous.  If delta H is negative and delta S is negative then the reaction will be depend on the temperature because this factor will allow you to figure out whether delta H or delta S is dominant. If both factors are negative then the reaction will be spontaneous only is delta H is dominate. If both factors are positive then the reaction will be spontaneous only is delta S is dominate. Polymers are molecules made go long strings of monomers that are attached to each other. In simpler words, rubber bands! Entropy and enthalpy also play a role in understanding these. In the lab we saw the rubber band contract and stretch. When the band is stretched the enthalpy is lower and the entropy is lower because when it gets stretched the molecules move into straight lines. Therefore, less disorder. When the band is contracted the enthalpy is higher and the entropy is higher because the molecules are very disordered. The Entropy is favored in a contracted band and the enthalpy is favored in a stretched band. In nature the contacted state is favored. This makes sense because when a rubber band is stretched it wants to contact. We don’t see a rubber band randomly stretch. That would be pretty weird, but kinda cool i guess. Temperature also comes into play. An increase in temperature causes the band to contract. Polymers are very useful in the medicine field. Before i end this blog i would like to point out that it is in fact my last blog and I know what your all thinking, “How can the world deprive us from this amazing knowledge?” I get it. Throughout my whole chemistry experience i have learned ALOT and i mean ALOT. Chemistry is everything we cannot see and how it works. Its likes a whole other world that is very fascinating! 

Chem Talk

In the lab we worked with a chemical reaction that continued to occur on its own once it started. This is called a spontaneous reaction. We also saw the factors how time played a role in the reaction. Our reaction consisted of producing heat energy. Knowing when reactions can occur spontaneously and knowing what can be done to speed up or slow down a reaction can allow you to control the reactions. This is what chemists and engineers do! Specifically, one set of theories called thermodynamics is used to answer the question “Can a reaction occur spontaneously?” A second set of theories called kinetics i used to answer the question “How fast can a reaction occur?” These sets of theories are pretty amazing because they are a huge piece in helping chemist and engineers change our lives. First, lets talks about spontaneity and thermodynamics. There are two factors that affects this. One being whether it give off or absorbs heat energy when the reactions occurs and two being whether the particles becomes more disordered or less disordered. If a change both releases energy and increases in disorder then the reaction is with out a doubt spontaneous. If a change both absorbs energy and decrease in disorder, it is clearly non spontaneous. If one factor is favorable and the other is not, telling whether it is spontaneous or not depends on whichever one is stronger. Now, lets talk about heat energy changes. Enthalpy is the change in heat energy and its symbolized by delta H (The change in energy). In a basic chemical reactions bonds in the reactants break and new bonds form to make products. When breaking bonds, they require an input of energy. This is known as a endothermic change. When forming bonds, you release energy and this is known as a exothermic change. The change in H is the products – the reactants and it allows us to predict whether or not the reaction is exothermic or exothermic. If delta H is +, then endothermic. When looking at an energy graph for an endothermic reaction, you can see that the energy of the reactants is lower then the products. The reaction is absorbing heat energy. If delta H is -, then exothermic. When looking at an energy graph for an exothermic reaction, you can see that the energy of the reactants is higher then the products. The reaction is releasing heat energy. Since bonds must be broken regardless of whether it is an endothermic or exothermic reaction, an activation energy much be obtained by the molecules in order for them to break and undergo a reaction. In a energy graph it is measured from the reactions to the “bump” of the graph. We talked a little bit about speed earlier, so lets bring that topic back. A catalyst is a substance that provides a lower energy pathway which allows for a reaction to increase in speed. In the lab, the iron is what played this role and allowed for the reaction to speed up and therefore generate us heat quickly. 

Chem To Go

  1. KF and Na2SO4 would conduct electricity because they are ionic bonds.
  2. Water does not conduct electricity, but it is an electrical conductor, so it would not be a good idea to mix water and electrical appliances. It would not be safe. Our bodies are also electrical conductors, so thats why we get shocked when all of this is mixed.
  3. Probably. 
  4. Anything lower than zinc on the chart because they will all oxidize with copper and will have a higher voltage in doing s0.
  5. Voltage would decrease – Voltage would decrease – Voltage would decrease – Probably stay the same, but eventually decrease.
  6. The conductivity decreases.
  7. (C) Au ^3+ + 3e- –> Au
  8. The numbers lost is always equal to the number gained

Chem Talk

You may have heard that when you have the stomach bug, it is important to drink gatorade or pedialyte because they have a lot of electrolytes. Well, electrolytes are substances that dissolve in water to make solutions that conduct electricity. For the solution to conduct electricity, charged particles must be present and they must be able to move around. Ions are a positively charged particle or a negatively charged particle. In the lab all the solutions we tested dissolved in distilled water, but only the substance that broke into charged particles when dissolved were electrolytes. On the other hand, molecular compounds do not break up into ions when they dissolve in water. For example, sugar remains a sugar molecule even when it dissolves. Since molecules don’t form charged particles in solutions, we can conform that molecules dissolved in water don’t conduct electricity. Non electrolytes are are molecules that do not form ions in a solution. A battery is composed of two half cells. One cell included the anode which is where oxidation takes place. The other is called the cathode and this is where reduction takes place. In our lab electrons are produced by oxidation of sins metal at the anode. Zinc ions enter the zinc nitrate solution and the electrons go through the wire until they eventually reach copper metal electrode where reduction takes place. We then know that the copper metal electrode increases in mass. This was the reddish substance surrounding around the copper. In a battery electricity only runs spontaneously in one direction. The activity series helps us understand that zinc is more reactive. Zinc reacts spontaneously with copper, but it would not work the other way around. 

Chem Talk 5

In todays lab we further examined the colors that make up visible light. We also explored LEDs and how they relate to glow in the dark light. Light is a form of energy known as electromagnetic radiation. In addition to visible light that we can see, electromagnetic radiation includes gamma rays, X-rays, ultra-violet rays, microwaves, and radio waves. Light is characterized by its wavelength and its energy. The wavelength go light is the distance between two corresponding points and its measured in nanometers. Gamma rays has the shortest wavelengths and radio waves have the longest wavelength. All waves of light travel at the speed of light. So, in other words, VERY FAST! The wavelength go light is also related to another property of light which is frequency. The frequency in waves per second X the wavelength in meters = the speed of light. Wavelengths that are long tend to have a lower frequency. This means Gamma rays have the highest frequency and energy and radio waves have the lowest frequency. The energy of light works this way too. The energy which is measured in joules = Planck’s constant which is 6.63 X 10^-34  X  frequency. Red light has less energy then purple light. This also helps us to understand why the red LED didn’t produce a glow in the dark star and the purple one did. Now lets talk about where the light comes from in the first place. When electrons are given energy they go from their ground state to an excited state. Eventually it wants to come back down so in order to do so, the electrons need to loose energy and this is where they let out light. The distance from the ground state to the excited state is what color light the electrons will give off. Each color has a different distance! Fluorescence and phosphorescence are two different ways light is emitted. Fluorescence is what we see when we see the LED light up. The electrons go up and down quickly allowing us to see the light. Phosphorescence is what we saw when we saw the green glow in the dark dot. The electrons quickly go up and then go to a forbidden state that is called the triple state. I mean it is suppose to be forbidden, but the electrons go there anyway. The electrons get stuck here and then its a slow process down back to the ground state and this is where the green light was emitted. 

 

Chem Talk

Metals are shiny objects with important properties. Some properties include being able to conduct electricity and heat, withstand high temperatures, and be able to take different shapes. This mean that they can be used in wires, cookware, and be pounded into different shapes to make tools and such. The periodic table is made up of many metals! They are all on the left side of the staircase. Most of these metals don’t occur naturally as pure metals in nature and most are reactive. Throughput time, chemists have been experimenting with the activities of metals, and it was discovered that some metals react more easily with most ion solutions than others metals do. The activity series was then devolved and it consisted of observations. The reactions that occur between metal atoms are called oxidation-reduction reactions. Oxidation is defined as giving up electrons (ex. Zn à Zn^2+ + 2e-). Reduction is defined as receiving electrons, which is basically the opposite of oxidation (ex. Zn^2+ + 2e- à Zn).  When your talking about 2 different elements and one is oxidizing and one is reducting, you can balance the redox equations. One thing that is confusing is the fact that hydrogen is included in with metals when it is clearly not a metal. It is only included with the shiny hard things because hydrogens role in strong acids make the acids simple and convenient reagents which then can quickly establish where an unknown metal stands in the series.

Chem Talk 3

“Dozen” is a word we use to say a specific amount of something, like a dozen donuts or eggs which would imply that there is 12. A mole is also a word that represents a specific amount of something. One mole is equal to 6.022 x 10^23 or in other words a VERY VERY big number. We use moles when talking about atoms and molecules. One mole of any single kind atom or molecule has a mass equal to its atomic or molecules mass expressed in grams. For example, one mole of oxygen atoms has a mass of 16g. The 16g is the molecular mass of oxygen atoms. One mole of oxygen molecules is equal to 32g because an oxygen molecule is O2 and 16 x 2 = 32g. When looking at compounds, you can add the molecular masses of all of the elements involved to find the total for the compound. Also, one mole of almost any gas at standard temperature and pressure will occupy the same volume – 22.4 L. One mole of gas at room temperature will be a bit larger because when the temperature of a gas increases, the volume of the gas also increases. Stoichiometry is when one calculates the number of moles of one chemical in a reaction based on the number of moles of one of the other chemicals in the balanced chemical equation. In a balanced equation, the coefficients are what set the proportions and they relate the number of moles between the products and the reactants. Lets use the balanced equation N2 + 3H2 -> 2NH3 as an example to explain all of this. You have 3 times as much of one of the starting materials, so you need to calculate that equivalent in the products.                                                             3 moles of N2   X   2 moles of NH3      =      6 moles of NH3                                                                     ————————–                                                                       ____________1 mole of N2                                                                                   With the Stoichiometry method, you can covert a known mass or volume of chemicals into moles and then convert it back. To solve a Stoichiometry problem, you have to first figure out what measurements you are beginning with and what measurements you want to end up with. Then, you find ways to convert between one unit to another, and this is where the dominos come in. Its like what we did earlier! As you write out your dominos, you will see that your units cancel one another out. In the first domino, what you are talking about (Ex. N2) should be the same in the bottom of the next domino. The number does not have to be the same, but the unit does. When one does a reaction, it is possible for the product to have lost small amounts. This is why scientists give a percent yield for a reaction. The percent yield is the trio of the product recovered to the product expected, and it is shown as a %.                                                       Say you have a reaction wth 134 L of NH3 and only 121 L got recovered. You would do the (Volume/Mass Found) / (Volume/Mass Expected) X 100%. So, 134/121 x 100% = 90.3% Yield! The Stoichiometry method is very present in the real world and will help our world continue to develop. 

Chem To Go

1)

a. The tablets are going through a endothermic change due to the bonds breaking.

b. The water vapor is going through a exothermic change due to the bonds forming.

c. The copper is going through a exothermic change. 

2)

  • (1) The particles increase in disorder because they are going from a solid to gaseous state. 
  • (2) The particles decrease in disorder because they go from water vapor to liquid droplets which shows that the particles became more formed.

3)

a. Reacents: Solid Iron and Oxygen Gas 

Products: Iron (lll) Oxide gas

Reacents: Potassium Clorate 

Products: Potassium Clorite and Oxygen Gas

b. (1) Decrease in disorder because the reactants are solid and gases and the product is just solid, so it became more formed

(2) Increase in disorder because the reactant is solid and the products are solid and gaseous, so it became less formed 

4) C. 

5) D.

6) A.

 

Chem Talk: Energy And Entropy

In today’s lab we looked at different methods of something that had the same outcome for our future Rube Goldberg machines. Each method produced CO2 gas which then blew up the ballon and moved the ruler. Each method also required different materials and all took different amounts of time. It was found that 2 were efficient, quick, and manageable. The other 2 were found to not be so practical due to the time it took and materials that were incorporated. When matter goes through a change the energy will get stored or placed in one form to another form or place. No matter what, the total energy that is in the universe will stay the same because the energy cannot just disappear or appear, it just needs somewhere to go and come from somewhere. When energy is added, the piece of matter goes from a lower energy state to a higher energy state, and when energy is released, the piece of matter goes from a higher energy state to a lower energy state. When energy is added to something, the energy from start to end in the chemical is positive one. This is called an endothermic change. When something releases energy, the change in energy of the piece of matter is negative. This kind of energy change is called exothermic. In our lab there were two methods that needed to have energy added. These were endothermic reactions! The particles in matter are what increase and decrease in energy. The particle rearrange as they go through a change. For example, in situation A say there are 20 particles that are neatly lined, light packed, and not having much room to move around in and in situation B there are still 20 particles, but a little more spread out with some room to move around in. Chemist call the movement of particles from A to B increase in disorder and from B to A decrease in disorder. Wow… original right? Chemist quantify disorder under the same of entropy. This given the symbol S. Bonds exist within the molecule and hold the atoms in each molecule together. Attractive forces exist between molecules in solids and liquids and they hold the molecules of the solids and liquids. For example, in water it takes energy to break or form the attractive forces in water molecules. When the forces break or form, we then see the state changes that water goes through (liquid<>gas). Overall, the lab was a lot of fun and gave me some ideas for our future project.