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Chemistry is the study of matter.
Matter is anything that:
1. Takes up space- volume.
2. Has weight- mass.
There are different forms of matter. Everything in this world is made up of matter. The smallest ingredient of matter is an atom. Elements are different types of atoms. There are 103 different types of elements. Different combinations of elements make up the many different things in this world.
Compound- group of two or more atoms put together. The atoms stay bound as a compound forever. Only a chemical reaction can break them apart. Elements, however, never change no matter what you do to them.
Examples of chemical reactions:
1. If you burn a piece of wood-
2. Piece of toast- the toaster burns the outside of the bread and it detaches. The burnt part is made up of carbon.
3. If someone would eat sugar and then be active, the sugar would come out when the person breathes as carbon and water.
A mixture is when to different things are physically touching each other. There are two different types of mixtures:
1. Heterogeneous- not a perfect mixture. Example: salt and sand.
2. Homogeneous- a perfect mixture, where everything gets evenly distributed. The only way to achieve such a mixture is with water- aqueous mixture.
The only way to make a mixture is by physically putting it together. Physical separation is the only way to separate a mixture.
1. Salt and sand- sift.
2. Mix of different vegetables- by hand.
3. Water and salt- evaporate the water. The changing of phases is a physical change because the compound doesn’t change.
Energy- the ability to do work.
There are many different forms of energy:
1. Kinetic energy- how fast something is moving. This is based solely on temperature- the greater the temperature, the more kinetic energy.
2. Solar energy- from the sun.
3. Potential energy- anything with energy stored in it. Example: sugar, batteries…
4. Nuclear energy
5. Electric energy
6. Heat energy
7. Hydro energy
8. Light energy
9. Chemical bond energy
Law of conservation of energy- energy is never created and energy is never lost. Energy is transferred.
There are two types of reactions:
1. Absorbs or needs energy to work.
2. Gives off energy.
Endothermic reaction- takes in heat in order to work.
Example: as ice cubes are absorbing heat,
and therefore melting, an endothermic
reaction is taking place.
Exothermic reaction- releases heat.
Example: When placed in a freezer,
a cup of warm water gets colder and
colder because the heat is released.
When an endothermic reaction takes place, an exothermic reaction occurs, too.
Example: an endothermic reaction
is occurring to the ice cube and the
an exothermic reaction is occurring
to the water.
Endothermic reaction: A+B+ heat→ C, H2O(s) +heat→ H2O (l)
Exothermic reaction: X+Y→ Z+ heat, H2O (l) → H2O(s) +heat
Hint: By an endothermic reaction, when heat is absorbed in, you write “heat” inside the arrow. By an exothermic reaction, when heat is released out, you write “heat” outside of the arrow.
A thermometer is used to measure heat. The scale used is that of degrees.
Example: if a thermometer would be put into
a freezer, the thermometer would be the
hotter object. As heat is released from it, the
mercury begins to move slower and slower and
it takes up less room. If the thermometer would
be the colder object, it would absorb heat and the
mercury would take up more and more space.
They wanted that the thermometer should be the same for everyone, so they marked freezing point and boiling point. Freezing point is 0°C and 32°F. Boiling point is 100°C and 212°F.
Kelvin Scale- felt that 0° isn’t a low number. Negative numbers are much lower. But having so many negative numbers isn’t good as it complicates things. Absolute zero is a point on the Kelvin scale where theoretically, gas takes up no volume. This point is at 273°C. This is only theoretical because when it really gets that cold, gas changes phases. On the Kelvin scale, Absolute zero is 0°. Freezing point is 273° and boiling point is 373°.
The degrees in Celsius and Kelvin both move at the same interval.
Calorimeter- an enclosed container which measures how many calories are absorbed or released by a chemical reaction.
Example: the water measures 25°C. A reaction
vessel is inserted into the water. After the
reaction occurs, the thermometer measures
19°C. The reactive vessel was absorbing heat
and an endothermic reaction occurred.
A calorie is a measurement of how much energy we get from something. One calorie is how much energy is needed to raised one gram of water by 1°C.
Calorie= grams of water x change in temperature.
100 grams, 50°→ 60° 10 X 100= 1000 calories.
200 grams, 30°→ 25° 5 X 200= 1000 calories are absorbed.
1 calorie= 4.18 (4.2) joules.
J= grams of water x change in temperature x 4.2, J= mass x ΔH x 4.2
Heating curve- shows how a substance changes phases.
Water at -50° is at a sub zero level and is freezing. It begins to heat up and it gets warmer and warmer. It is absorbing energy. At 0°, the molecules can start separating and they are at the right temperature to break apart and melt. However, there is an attraction holding these molecules together and before they can separate, the force has to be broken. It breaks by the absorption of energy. The water keeps absorbing and absorbing (but it is not getting warmer), and then the molecules break apart and the water begins to melt. Once it hits a liquid form, it gets warmer and warmer until it hits 100°. When the water hits 100°, the water is hot enough to start turning into a gas, but the attractive force doesn’t let. (Water never gets hotter than 100°.) It absorbs energy to break the attractive force and when enough energy is absorbed, it changes phases. This phase change from a liquid to a gas is called vaporization. The actual pot of water is at 100° and all the energy is causing water to jump out of the pot. Once the gas is out of the pot, with a source underneath it, the temperature can rise.
How much energy is needed to cause something to melt? 334 J/g. Melting is known as fusion. The heat of fusion is 334 J/g. The heat of vaporization is 2260 J/g.
Cooling curve-
At 100°, gas begins to condense. It has too much energy though, and has to loose the extra energy that it gained. It has to lose 2260 J/g. When all the energy is released, it is a liquid. The water gets colder until it hits 0°- freezing point. The water loses 334 J/g and only then it can freeze.
Sublimation- when a substance goes from a solid directly to a gas and skips the liquid phase. Why does this happen? Because the substance is forced into the solid form. As soon as it is released, it goes back to a gas. Examples:
1. Dry ice- CO2(s)- when carbon dioxide is frozen so cold and put under tremendous pressure, the molecules slow down and go together and it becomes a solid.
2. Iodine crystal- I2(s)
