Chemistry Standard 7b

Chemistry Standard 7b: Students know chemical processes can either release(exothermic) or absorb (endothermic) thermal energy

The term exothermic describes a process or reaction that releases energy usually in the form of heat, but also in the form of light(flame, explosion, spark), electricity(battery), or sound. Chemical exothermic reaction are generally more spontaneous than endothermic reaction. In a thermochemical reaction that is exothermic, the heat is placed on the products of the reaction.

The opposite process is endothermic process which absorbs energy in the form of heat. Chemical endothermic reaction need heat to be performed. In a thermochemical reaction that is endothermic, the heat is placed on the reactant side.

Some examples of exothermic processes:

• freezing water
  
• condensing water vapor
  
• combustuin of fuels such as woods, coal and oil
  
• mixing alkalis and acids

Some examples of endothermic processes:

• melting ice cube
  
• evaporating liquid water
  
• converting frost to water vapor(melting, boiling and evaporation in general are endothermic processes )

exothermic reaction video

endothermic reaction video

making play-dough

Materials:

• 1 cup of flour


• 1 cup of water


• 1/2 cups of salt


• 1 table spoon of oil


• food color

Procedures:

1. Put flour, water, salt, and oil in the pan and mix them together.


2. On low temperature, put food color and stir them together


3. when the mixture becomes solid, turn off the burner so it can be cool enough to touch

Tips:

• sit the mixture on low temperature


• don't go to burner too close


• watch your hand when you stir the mixture

Science:

In play dough compound, surfactant combines with lubricant to reduce stickiness

photocredit: Theresa Anselmo

Bending Glass

I bent and twisted the glass today.

Tips:

• Don't bent the glass back and forth. It will make glass break.
• place the glass closely on the burner. It might take time if you place it too high.
• wear goggles and gloves for your safety
• Use two holders when ypu bend the glass

Science:

Glass is a visco-elastic material whose mechanical properties change very rapidly over a small temperature. so even though there isn't very high temperature. glass easily bends.

Photocredit: Kayla Jonansen

toothpick in the balloon

I stuck the toothpick in the balloon

Tricks:

• the smaller balloon you have, it's easier than bigger ones
• Use sharp toothpick so that can go into the balloon easily
• put vaseline on top of the balloon so it can make it smooth
• Stuck the toothpick on the very top of the balloon where has thickest rubber

Science:

Because of balloon's flexibility, balloon easiliy pops. But if you try on the top, rubber can easily move. so if there is more rubber, it's easier to stuck the sharp objects.

photocredit: Theresa Anselmo

Mills Canyon Field Trip

큰 지도에서 Mills Canyon Field Trip 보기

cutting and bending glass and putting toothpick in balloon

This week we did two experitmentsl, bending glass and putting toothpick in ballon.

We wore goggles for our safety and cut the glass before we burn the glass.

We used nail file to cut the glass. After we made damage in the glass, we broke the glass whcih faced downward. Then we put glass above the fire and made glass melt and bend slowly. We had to be careful because it might burn your fingers. It was interesting experiment.

We blew the balloon and tied the top. And then we picked the sharp toothpick and put vaseline on the balloon and toothpick. We were scared to put the toothpick in the top of the balloon so we asked someone else to do it for us but he also failed. I regreted after him by not trying. I could success instead of him. Anyways, I knew tht balloon could hold sharp thing on the top of the balloon.

IProposeWe

Link: Make Ice Cream in a Baggie

Materials:

• 1/2 cup of milk



• 1/2 cup of whipping cream



• 1/4 cup of sugar



• 1/4 teaspoon of vanilla or vanilla flavoring



• 1/2 to 3/4 cup of sodium chloride as table salt or rock salt



• 2 cups of ice



• 1-quart ziploc bag



• 1-gallon ziploc bag

Procedures:

1. Add 1/4 cup of sugar, 1/2 cup of milk, 1/2 cup of whipping cream and 1/4 teaspoon vanilla to the quart-ziploc bag. Seal the bag securely.
   
2. Put 2 cups of ice into the gallon-ziploc bag.
   
3. Use a thermometer to measure and record the temperature of the ice in the gallon bag.


4. Add 1/2 to 3/4 cup of salt to the bag of ice


5. Place the sealed quart-bag inside the gallon bag of ice and salt. Seal the gallon bag securely.


6. Gently rock the gallon bag from side to side.


7. Continue to rock the bag for 10-15 minutes or until the contents of the quart bag have solidified into ice cream


8. Open the gallon bag and use the thermometer to measure and record the temperature of the ice/salt mixture.


9. Remove the quart bag and enjoy your ice cream.

Safety Precautions:

Wear gloves when you rock the gallon bag. It might damage your hand

Scientific Principles:

Ice absorbs the energy in order to melt. the energy is absorbed from the ingredients and from the outside environment. When you put salt into the ice, it lowers the freezing point of the ice so more energy can be absorbed. Ice gets colder and this is how your ice cream freezes.

proposal for activity

I want to do the experiment like you did with aluminum balls.
It made sparks when you hit the balls together. It was short but strong.
I heard Mr. Paul's class made a icecream. I want to do that too.
I want to do something big! hahahaha
ex) black snakes or glow worms
colored fire spray bottle
fake snow
green fire
ice cream in a baggie
colored smoke bomb
glow in a dark slime
making glass

Gases

STP tells us that 1 atmosphere is 273K. When we do the problems, we have to change the variables of temperture to Kelvin.

For equation PV=nRT, P is pressure(atm, kPa), V is volume(L), n is number of moles(mol), T is temperature(K) and R is a gas law constant. R is always constant and it has value of .0821(L atm)/(K mol).

The important thing that we hace to remember is that volume of 1mol He at stp is 22.4L.

I also learned that higher attitudes have less air pressure. And at a given T, lightest molecules move fastest and heaviest molecules move slowest.

Charles' Law abd Gay-Lussac's Law tell us that they are both directly proportional.

Equations for both Laws are V=kT and P-kT.

The combined gas law is P1V1/T1=P2V2/T2. They also have to use temperatures as in Kelvin, too. To change the Celcius to K, you just have to add 273 to the Celcius temperature and that will make you to have Kelvin.

David Webb and Vacuums

We had special geuest speaker. David Webb showed us many experiments with Vacuums.

First, he showed how the pressure helped people in the old times. He said it was used since a really long time. People use to get a water from a Nile River to upper land. It was pretty interesting that they knew the pressure.

Vacuum had plastic case above and when vacuum started to work, vacuum made pressure lower. when the pressure got lower, the objects went bigger.

There was balloon experiment. He placed the balloon with air in it. When the pressure got lower, the balloon got bigger and finally popped. When they placed a marshmallow, it became bigger. He stopped the vaccum and reput the air in it. I thought the marshmallow will gonna become normal as before without thinking. But marshmallow was flatter than before and it was hard to chew.

He showed us experiment with leather and object that looked like metal which was much more heavier thatn leather. When he placed both objects and made them fall, they fell at the same time.

Gases

There are three state of matter, solid, liquid, and gas.

And we are learning about gas now.

Gases may be harmful but it is also useful.

Gases are bouncing each other like billiard balls. They always move and moving molecules have kinetic energy.

Evangelista Torricelli developed BAROMETER in 1643 which measures pressure of air. It contains column of mercury. He found out that s standard atom ha 760 mm Hg.

We had experiments about pressure. When we put more pressure in the water bottle, the eyedropper inside the bottle went down and it showed how divers dive in the ocean. And the other experiment was that when we put more pressure in the bottle which had nothing but small balloon, the balloon got smaller and flatter.

Equilibrium

Chemical Euqilibrium is dynamic, reversible, and have forward rate and no change in concentrations.

Factors that affect reaction rates are temperature, concentration, particle size and catalyst. Euilibria resist change according to the Le Chatelier's principle.

When you increase the temperature and pressure, you'll have more products. But if you decrese them, you will have less. When heat is a product, it is exothermic reaction. And when heat is a reactant, it's endothermic.

thermochemistry II

We had a several experiments which were related to thermochemisty.

We boiled the ice cube and change the state of matter. We kept watch the temperature of the substance until it disappered into gas. It increased the temperature when they don't change the matter but it stayed constant when they changed the state of matter.

We also had elephant toothpaste experiment. I really wanted to see this since I saw the video. It was really cool. It just turned yellow and popped up with high temperature.

We also did alot of thermochemistry problems. It was pretty difficult to find all the temperature and add all up when there are cold and hot water which become solid to liquid to gas. There are many formulas you can use while you solve them, like latent heat of vapor and fusion of water. Latent Heat of Fusion of Water is 80cal/g and Latent Heat of Vaporization is 540 cal/g.

Thermochemistry

Thermochemistry is the chemistry of energy.

For exothermic reaction, delta H is negative and for endothermic reactions, delta H is positive.

Equation is Q=MC delta T.

Q represents energy, M represents mass, C represents heat capacity and delta represents change in temprerature.

Heat capacity is the amount of energy required to raise the temperature of 1g of X by 1 degree C. And delta T is final temperature minus initial temperature.

1cal is about 4.184 Joule and it is from James Prescott Joule who found this unit.

reaction1

In the chemical equation, there are reactants and products. We can put (s)(l) or (aq) which are the symbols solid, liquid, aqueous. And the arrow between reactants and products means "yields" or "produce".

There are ficve reaction types: Synthesis, Decomposition, Single Replacement, Double Replacement and Combustion. And when there are reactions between two solutions, you will see that there are color change or bubble form of heat is absorbed ro released.

Solids form precipitation.

When you balance the equation, you can use coefficients to balance both equations.

acid and base

Acid has strong sour taste and base has bitter taste. They can be neutralize by forming salts.


the water is pH scale 7 which is neutral.


We can see which is acid or base by the indicator. indicator changees color blue to red if it's acid and red to blue if it's base.


strong acid has more H ions and strong base has more OH ions.


Example of strong acid is Ammonia and storng base is Sodium Hydroxide

To find the MOlarity is mol/liter
and it's really useful if you know M1V1=M2V2, which shows masses and volumes of two solutions.

stoichiometry

In chemistry, there are many reactions. I saw reations between gas bubbles with fire and between magnesium with fire. When we finished burning magnesium, the mass of magnesium became less than before.

These reactions were really interestion and caught my attention.

Stoichiometry calculate reactants and products. It is also about the mass, moles of two property. I learned formulas which was g x to mol x to mol y to gram y. It was pretty complicated. We had to get a mass and calculate before we do the real calculation. The mole has 6.022 x 10 to the 23power. I learned chemists are doing experiments with exact mass of element. I knew they didn't want to waste them. They calcutlated with periodic table. Periodic table has mass of one mole of every elements. So we could mass of mole easily by looking through the table.