In this section of Chem. Talk we refer to spontaneity, which is the change from the system to the surrounding or vise versa.
Enthalpy is one if the types of changes, and we covered the is class. This change is one the releases heat energy from the system to the surroundings. This means that the heat energy is being lost/given out which is an endothermic reaction. In class we were able to observe the hands on by conducting a reaction and taking the before and after temperature, along with feeling the test tube and the warmth it gave off. When heat is lost from the system this is known as a change in enthalpy resulting in a negative change. However, if the heat energy were to go from the surroundings to the system it would be the opposite. Instead of feeling the test tube being warm it would feel cold, as the heat is taken from your hand and absorbed by the system. This would be a positive change in enthalpy.
In class we also talked about entropy. This is the disorder a particle processes. Whenever a reaction/change occurs the particles change order (becoming more or less organized). The entropy increases when the system is more disorganized and the entropy decreases when it is more organized.
The experiments we did in class really helped put this Chem. Talk together because it was very hand on as you could actually feel the change in the enthalpy on most of the reactions. It was nice to conduct this and then read about the details that we might have missed in class and really understand the whole picture.
In this section of Chem. Talk we are going to be investigating a reaction that continues to occur on its own, after it has begun. This type of reaction is called a Spontaneous reaction. We can also investigate how to control the speed of a reaction and the factors that control this aspect of reactions.
In order for Chemist to be able to control spontaneous reactions they need to know how fast/slow it will react and what will react. To do this there is a theory called Thermodynamics is used to answer weather a reaction can occur spontaneously, while another theory called Kinetics is used to determine how fast a reaction will occur. Putting these two theories together allows us to design reactions that impact lives.
There are two factors that infer weather or not a spontaneous reaction will occur. The first is if the change gives off heat, the second is if the parcels become less/more disordered.
This Chem. Talk was a good way to introduce the next topic but it kinda jumped around a bit, so i am looking forward to doing classwork/lab work tomorrow to see what i am reading about in person to clear it up.
Electrolytes are substances that dissolve in water, creating a solution that conducts electricity. In class we used a a circuit (consisting of wires and an LED light) to determine weather or not a substance was conducted electricity. In this section of Chem. Talk it informs us that in order for a solution to conduct electricity it must contain charged particles that are able to move around. All the solutions we tested in class we made of substances the dissolve in water but only the ones that broke into charged particles were able to be Electrolytes.
The battery is made up of two half cells (hence half cell reactions). The half cell where Oxidation occurs in the Anode while the other half where Reduction occurs is called the Cathode. Both are not able to exist without the other. If one is occurring the other must be as well.
Now you might be wondering why all this is important and what it has to do with the Activity Series. Well, The Activity Series determines which reactions are able to occur or not occur and the direction the electricity travels in (spontaneously or non spontaneously). Also, it determines how powerful the metal or metal ion reaction can be.
Reading this section of Chem. Talk really helped me understand what the experiment we conducted in class had behind it and how it all worked!
A couple weeks ago we learned about metals and the different properties the processed; so i think it is interesting how past topics we have covered always come back through another section in this class. It is helpful and causes you to use previous knowledge to understand new topics.
Today in class we learned about the activity series by doing a lab at the back of the class room. In this section of Chem. Talk it touches on how this series came to be. Back in medieval times alchemist experimented with different metals, trying to see which ones could create gold. Now we know this is not possible because you can not change the amount of protons and neurons an element has without changing the element; only the arrangement of electrons changes. However, in the process of these experiment the alchemist discovered that some metals react easier with most metal ion solutions than other metals do. This is how they created the activity series (by using their observations). Since then chemist have measured this more accurately.
The special reactions that occur between Metals and Metal ions are Oxidation ( giving up electrons) and Reduction (receiving electrons). However, when Oxidation happens a Reduction also occurs. Think about it, electrons that are given up also must be accepted by something. A reduction change and a oxidation change are often called Half changes for this reason.
Stoichiometry is a new concept to the Chem. talks but it connect to what we have learned before, throughout the year. For example, we studied ‘moles’ earlier this year. Moles are used for counting very large quantities of very small objects, just like a dozen is used to count twelve donuts. It always is the same number. Also, a mole is that one moles of each atom or molecule has a mass equal to its atomic/molecular mass. However, in Stoichiometry, moles are used during the calculation. The base of Stoichiometry involves calculating the moles of one atoms to another. Stoichiometry is, for example, the volume id carbon dioxide to blow up a ballon and also the amount of moles the reactants needed. All the topics we have covered so far in Chemistry are starting to relate to each other and connect. I am starting to notice this more clearly now and it helps to apply old topics in order to figure out the new ones.
1.) Polarity of molecules is the difference in charge across the given molecule.
2.) London dispersions are the weak intermolecular forces that causes the electrons in an atom or molecule to shift slightly in order to form a temporary dipole moment.
Chem. To Go
4. The intermolecular forces in water are stronger than those in methane
In class we have been creating 3D models of atoms and today we took it a step further, by putting them into categories based on their electron or molecular geometry.
Electron geometry is based on all electron domains (counting lone electrons as well).
Molecular geometry focuses on the bonding domains.
For example, this atoms in the photo below is Tetrahedral (electron geometry) and Pyramidal (molecular geometry).
During class we discovered how to create 3D electronic configurations, taking a 2D Lewis dot structure and building it in 3D. I learned that the shape and angles of the structures began to matter. There were Linear (180 degrees), Trigonal (120 degrees), Tetrahedral (109.5 degrees), Pyramidal (107 degrees) and Bent (104.5 degrees). I never knew the shape and angles would matter as they did not in the 2D structures.
By doing this class today, we had to review dot structures and the rules about them. 1 line between atoms represents a bond (the sharing of 2 electrons). There can also be double bonds(2 lines) and triple bonds (three lines). The electrons that are left over and not being shared, are called lone electrons or non-bonding pairs.
These classes were a good refresher on dot structures before leading up to the new challenge of making 3D models of them. It helped with my understanding of the topic.
Through reading this Chem. Talk I learned that most reaction take place in water (aqueous) and that when certain Cations (+) and certain ions (-) are combined, water-soluble ionic compound are able to form. But the these ions are in separate aqueous solutions and then combined a precipitate is then created. A precipitate is an ionic compound.
In a ‘real-life scenario’ this is used to create paint. The precipitate we observed in our lab can be used as the pigment in paint. The pigment is crushed into a powder and then mixed with liquids (linseed oil, turpentine, guar gum, water…etc.). The id the pigment is in-soluble in the liquid it becomes a suspension of particles in the liquid it was added too. The when the paint dries, the liquid is gone and only leaves the pigment particles (the color) behind. I had no idea this was how paint was made and found it cool how we observed this on a smaller scale in class during our lab.