Here’s an awesome prezi Erin made, which describes the phases of matter. What I’d like to include is this:
Latent heat of vaporization is used for vaporizing and condensing, it’s just a matter of what the energy is coming from.
Same applies to the latent heat of fusion, which is used for melting and freezing
First, let’s review. Remember, we describe energy by what it does, not what it is. So when something has energy, it has the ability to do work.
How do we describe heat energy?
Heat energy is transferred among substances because of temperature differences.
Now let’s learn how to measure/ calculate heat energy:
Here’s a new term: SPECIFIC HEAT CAPACITY. What’s that?
Heat necessary to change temperature = mass × specific heat × temperature change
H = mc(Tf - Ti)
Now let’s try one:
How much heat is necessary to make the temperature of a 100 kg. bucket of water drop from 17 C to 13 C?
When you cancel out the units, you are left with 400 Kcal needed to change the temperature just 4 degrees. This shows us that an INCREDIBLE amount of energy is needed to change something’s temperature.
However, sometimes adding heat doesn’t change the substance’s temperature, or kinetic energy of its molecules. How? When something is undergoing a phase change, the heat energy doesn’t change the substance’s temperature. Instead, that energy goes into breaking the molecular bonds, rather than changing the molecular speed.
We call this latent heat. Latent is latin for “hidden”, as latent heat is in a sense hidden since is doesn’t appear to change a substance if you look at a thermometer.
As shown here, energy is constantly being put into this substance. But once it reaches a certain temperature, it makes a very abrupt stop in the rise of temperature, and all the energy goes into changing phases. Once it is COMPLETELY done changing phases, the temperature will continue to rise again.
So, when solving for the heat needed to change phases, we need to know the specific latent heat for the substance. There are different specific heats for each phase change. Here’s a chart that lays out some of those numbers:
Recall that the heat of a substance is also dependent upon its mass. With that in mind, let’s look at the equations for latent heat
In more simple terms, this is H = mL. So, let’s try a problem involving phase and temperature changes.
How much heat energy would be lost from someone who puts their hands on a 0 C ice cube that weighs 2 kg, and it melts into 40 C water?
Now, add 80 kcal and 160 kcal together to get 240 kcal.
Today, we’re going to discuss what acids and bases are, and how they are measured on the pH scale.
The pH scale goes from 0 to 14, 7 being “neutral.” Anything from 1 to 6.99 is acidic, and anything from 7.01 is basic. The closer something is to 0, the more acidic it is, and the closer to 14 it is makes it more basic.
We measured ph with litmus paper, which, when reacted with an acid or base, turns a certain color as a result of a chemical reaction. The above colors are displayed on the litmus paper whenever it is coated in an acid or base.
But what exactly are acids and bases?
Basiclly, acids have much more hydrogen (h+) and bases have more hydroxide (OH-)
For example, lye is a base because it has more OH- than H+
Today, we’re going to talk about how the chemical reaction between aluminum and copper (2) chloride in a solution of water. First of all, what is aluminum? What is copper chloride?
Aluminum is a metal that is very chemically reactive, and not very dense.
Copper Chloride is a blue powdery compound formed between the metal copper and the nonmetal chlorine.
In order to create this chemical reaction, we formed a solution of copper chloride and water. The water actually splits apart the ionic bond between the copper and the chlorine.
But how does it do that?
The copper is a metal, so it is going to transfer an electron to chlorine when they bond, so both become ions, which creates this ionic bond. Now, water is made up of what’s called polar molecules, which are covalently bonded. But unlike most bonds, polar molecules are actually “electrically lopsided.” So it may be neutral, but one end is more positive and one end is more negative. Anyways, when the ionic bond is submerged in water, the positive copper ion is attracted to the negative sides of the water molecules, and the opposite happens for the negative chlorine ions. But the main point is that the bond between the ions cannot hold them together any longer.
So we have our copper and chlorine solution, and then we add aluminum. What is about to happen is called a single replacement solution, which is written as
A + BC (arrow) B + AC
A reacts with a compound of B and C to produce B and a compound of B and C
With that in mind, the copper and the aluminum replace each other. Aluminum dissolves into the water as it bonds with the chlorine to make aluminum chloride, and the copper comes out of solution, which is why the aluminum appears to be missing, and there is pure copper at the bottom of the beaker.
Why is there left over aluminum in some beakers, but none in others?
Well, whenever a chemical reaction happens, the reactants and the products will always be in the same amount, meaning no matter can be created or lost. So, if there is a little copper chloride, it will replace only a little aluminum. And if there is a lot of aluminum, it will replace a lot of aluminum. With that said, the more copper chloride you added to the solution, the more aluminum that was replaced.
There are three methods that heat can be transfered, which are convection, radiation, and conduction.
Conduction is the transfer of heat from one substance to another through molecular collisions. Solids are generally better conductors than liquids or gases since their molecules are closer together and collide more often. That is why we call liquids and gases thermal insulators. Examples of conduction are tea kettles, cooking any food on the stove, or even melting ice with your hand. When you touch it, the heat energy travels from the warmer source (you) to the colder source (the ice).
Convection is similar to conduction in the fact that it needs a material medium to transfer heat, but it doesn’t do so through solids. Rather, it is the transfer of heat by movement of a substance from one position to another, usually through liquids or gases. Here’s how it works:
The lava lamp works just like the explanation above.
The last method of heat transfer is radiation. Unlike convection and conduction, it doesn’t need a medium to transfer heat through. Instead, it is done through electromagnetic waves, which is exactly how the sun transfers energy to Earth.
Part A: Work
(Click on Images to Enlarge)
Before we can understand energy, we must understand work. So what is work? Work is the magnitude and distance traveled, in effect to a force applied. So basically, when a force is applied to something, that something should move, only if the force had ability to do work. So if no change in motion occurs, there’s no work done. Don’t understand? Let’s look at an example.
A weightlifter exerts a force on a barbell that causes it to be displaced. Since there was some distance traveled, work was done.
Work= magnitude, or distance × force
If the weightlifter exerts 200 N of force on the barbell, and it moves 2 meters, then he did 400 Nm of work. One Nm = 1 Joule (J).
If the weightlifter exerts 200 N of force on the barbell, but it doesn’t move, the math looks like this:
W= (200 N) (0 m)
Thus, showing us that if no distance travels when the force is applied, there is no work.
In this case, the weightlifter did 10,000 J of work, not 20,000. But he traveled 100 m across. See, when work is calculated, the magnitude (distance) and force must be parallel. Since he is lifting the weights in the vertical direction, the magnitude must be in the vertical direction as well for work to be done. Since the hill was 50 m. high, he did 10,000 J of work.
W= magnitude × force
W= (200 N) (50 m)
W= 10,000 Nm = 10,000 J
When doing work, a force is applied, so there must be a force acting back, remembering Newton’s 3rd Law. This is why, even if we’re not technically doing work, it feels like we are. For example, when you lift something, you are working against its weight. Or, if you push something on a table, you are working against friction, which is a force.