Chem Talk Section 8

Last class, we introduced a new method to determine the spontaneity of a reaction which is called the Gibbs free energy. The change of G= the change of H(when it is exothermic, H is negative, when it is endothermic, H is positive)- temperature* the change of S(the increase or decrease of the disorganization of the particles). If the change in G is negative, the change will be spontaneous at the given temperature. (It is favorable). On the other hand, if the change in G is positive, the change will not be spontaneous at the given temperature and will not be favorable. Unlike the other predicting method where the reaction can only be spontaneous in certain conditions, the Gibbs free energy can occur under any circumstances. If the change in H is positive and the change of S is negative then the reaction is not spontaneous no matter what the temperature. On the contrary, if the change in H is negative and the change in S is positive, the reaction is spontaneous. 

Polymers are molecules made of long strings of monomers that are attached to each other. Rubber band is one example that has polymers. When the rubber band is stretched, both of its enthalpy and entropy are lower. Because as we stretch it, the molecules line up and they are able to experience attractions to each other. When the rubber band is contracted, both of its enthalpy and entropy are higher. The rubber band is stretched when cooled, and contracted when heated. 

chem talk section 6

Electrolytes are substances that break into charged particles when dissolved in water and can conduct electricity. However, these substances must contain charged particles like ions and they can move around freely. Non-electrolytes are molecules that do not form ions in solution and can not conduct electricity because they do not form charged particles. 

Two half cells makes up a battery. One of them called anode which is responsible for oxidation, and the other half cell called cathode is where reduction takes place. In the lab, we used zinc and copper to put in the battery. Zinc experienced oxidation so it loses two electrons. The electrons of zinc then travelled to the reduction part where copper exists. Copper gains two electrons and formed neutral copper metal with copper ions, therefore, its mass increases due to the attachment of copper metal. 

Chem talk section 5

In this section, we learn about light. We used visible lights in our experiment, which is a part of the electromagnetic radiation. Human eyes are able to detect visible lights because of their wavelength, which is the distance between two corresponding point of a wave. All wave travel in the same speed, that is the speed of light. (3.00*10^8) We can also figure out the frequency of the light from the equation c(3.00*10^8)=λ(wavelength in meters)*f(freq). The longer the wavelength, the lower the frequency. Same goes with the energy of the light. The longer the wavelength, the lower the energy. Therefore, infrared light would have the longest wavelength but the lowest frequency and energy. Energy can be found using the equation E=h(Planck’s constant+6.63*10^-34)*f(frequency in s^-1). 

In order for an atom to emit light, its electron starts off in the ground state and needs energy for it to move up the energy level. If enough energy is given, it will reaches to its exited state. While absorbing energy, it will also release energy and drops down to a lower energy level, the energy it releases will be light in this case. This is called fluorescence. However, some light using a more complicated process called phosphorescence. The electron first needs to have enough energy to reach the excited state and later fall to the intermediate state where it can emit light like what we saw on the glow tape. The color like blue and uv will then have the ability to emit that color because they have enough energy. 

chem talk section 3

In this section, we learnt more about mole and how to calculate moles and the amount of substances needed for a reaction to occur. The mole’s mass is equal to its atomic number, this is also called its molar mass. Balancing equation is also related to moles. We need to make sure each molecule or element has the same mole on both side of the equation. If not, we need to add coefficient in front of the molecules or elements to help them balance.  

Usually, we calculate mole in STP (standard temperature and pressure). We also figured out what dominoes are. You have to make sure your equation will be able to cancel things out and left with the unit you want at last. This is called dimensional analysis. Sometimes during the experiment, some product are found lost, so scientists came up with the percent yield method to figure out what is the original amount of product. For volume, it is volume found/ volume expected For mass, it is mass found/ mass expected.

section3 chem to go

  1. a. CO2. b. It came from the carbonated water after we heated up. c. Yes. d. Yes.
  2. NaHCO3(23+1+12+16*3=84)+ HC2H3O2(1+2*12+3+16*2=60)→NaC2H3O2(23+2*12+3+2*16=82)+H2O(1+2*16=33)+CO2(12+2*16=44)  84+60=144  82+33+44=159
  3. a. 12g. b. 27g. c. 14+1*3=17 d. 40+12+16*3=71 e. 23+27+2(32+16*4)=242
  4. a. 18/12=2.5 b. 27*0.5=13.5 c. 17*2.84=48.28 d. 10.0/71=0.14 e. 49.5/242=0.20
  5. a. (left)K: 2  CI:2 O:6.  (right) K:2 CI:2 O:6. b. (left)2*40+2*35+16*6=246 (right)2*40+2+35+16*6=246 c. 1
  6. a. 1 b. 12+16*2=44g c. 2g d. 4g
  7. a. 0.025 mole  b. 

section2 chem talk

The law of conservation means chemical equations that are balanced. It is when the  amount or quantity of each element is equal on both side(the reactant side and the product side), so its matter does not change, no matter how significantly it changed its bond. 

Scientists have been struggling with this concept for a long period of time,  Nasiraddin Tusi started to talk about how matter itself does not change despite the change of its bond and shape. 

chapter 4 section1 chem to go

1.a. exothermic. Because effervescent antacid tablet released its energy to its nearby surrounding-water, causing it to bubble.

b. exothermic. The water released its energy to rerverse its state of matter. 

c. endothermic. Copper gains energy from the air to oxidizes.

2. a. Liquid- Gas increase in disorder.

b. gas- liquid decrease in disorder.

c. Not possible to tell. Because there is no change in state for copper. 

3. a. 4Fe,3O2,2KClO3 are reactants. 2Fe2O, 2KCl and 3O2 are products. 

b. The first equation is a decrease in disorder because it went from solid and gas (which is equivalent to a liquid) to a solid. The second equation is an increase in disorder because it went from solid to solid and gas(which is also equivalent to a liquid)

4. d

5. a.

6. a. 



chapter4 section1 chem talk

Since the total amount of energy in the universe is always equal, therefore, energy does not just disappear, it either get released or absorbed by substances. If energy is given to a substance, it can go into the molecules making the particles to move faster or it can go into the bond of the molecules. However, bond is different from attraction force. Bond exists in the molecules while attraction force exist in between two or more molecules holding them together. Of course, an attraction force is weaker than a bond. But they both require energy to break it apart. If the energy change from start to finish is positive, meaning we gained energy during the process, it is called an endothermic change. On the opposite, if the energy change from start to finish is negative, meaning we lost or released energy during the process, it is called an exothermic change. 

The state that changed from solid to liquid to gas has increased its disorder. We can say that its disorder increases, if it goes from gas to liquid to solid, we can say that its disorder decreases. The amount of disorder we measured is called entropy. 

Chem Talk Section8

Glass is usually made of a combination of silica, sodium and carbonate after it is heated and cooled down. The glass can be heat up and cool down really quickly, so it is hard to form shapes. Colors will be present due to the impurities in the metal. Metal oxides will be needed for colored glass, they absorb various colored light and then reflect into different colors. Reflecting to the lab we did, even though the colors were not obvious, we can tell different materials form different colors if observed carefully. 

Metallic oxides are materials that help glazes in ceramics gain colors. However, it is really hard to maintain the color because it depends on many variables. Glazes are suspensions of different clays and minerals in water, they not only produce pretty color but also form a protective layer on the ceramics. 

Chem talk section 6

Precipitates are formed when some cations and anions are combined because those ions attract each other very strong and turn into a ionic compound. Precipitates are insoluble in water meaning they will not dissolve in water and will later be separate and left behind when the liquid is gone. Ions that do not involve during the reaction of forming a precipitate are called spectator ions. By removing those spectator ions, we can form a new equation called net ionic equation. The book also listed several rules to provide information and help us predict the reaction of precipitation.