Atomic Theory

We all know that atoms are the smallest particles of an element and they have the same properties of the element. But thousands of years ago, scientists were experimenting and proposing different theories before the modern atomic theory was proven.

Aristotle proposed the Four Elemenrs Theory, which basically stated that matter was made of earth, air, water, and fire. This theory lasted for 2000 years but was rejected because it couldn't be tested and proven.

Lavoisier stated the first version of the Law of Conservation and Mass and the Law of Definite Proportions.
Proust later proved Lavoidier's Laws to be true.

These are the 5 points of Dalton's Theory:
1) elements are made of atoms, which are tiny particles
2) atoms of the same element are the same
3) atoms in different elements are different and can be distinguished by their weights
4) chemical bonds are formed by the joining of atoms
5) atoms cannot be created, divided into smaller parts, or destroyed

Dalton also found out that water was always made up of 11% hydrogen and 88%oxygen, no matter how many atoms of water there were.

J.J. Thomson's theory was the first to have positive and negative charges. He proved the existence of electrons with a cathode ray tube and measured the charge to mass (e/m) ratio of electrons.

Rutherford thought atoms had a dense, positive center with electrons surrounding the center. He figured out that atoms are mostly empty space.

Niels Bohr proposed that electrons surround the nucleus in different energy levels and that when an electron jumped to the next energy level, the atom released light.

The Modern Atom Theory
The atom is the smallest particle of an element and it has the properties of that element. There are 3 subatomic particles: protons (positive), electrons (negative), and neutrons (no charge).


Here is a detailed timeline of scientists that used their observations and experiments to come up with their own theories of the atom before our modern day atom theory was proposed:
http://www.timelineindex.com/content/view/1228

Enjoy this fun, but educational video!
The Atom Song :)

** Note: Remember our Atomic Theory Timeline assignment is due on Wednesday!**

Percent Yield

Percent Yield is the amount of product obtained in a chemical reaction
It can be determined by the masses used in a reaction and the mole ratios in the balanced equation.

A good website for self study:
http://www.chemcollective.org/stoich/percentyield.php

Example 1:

For the balanced equation shown below, if the reaction of 50.6 grams of Pb(NO₃)₂ produces a 74.2% yield, how many grams of PbO would be produced ?
2Pb(NO₃)₂=>2PbO+4NO₂+O₂

To answer this question, you use the mass ratio from the balanced equation to determine the theoretical yield.
theoretical yield of PbO:(mass of PbO)/(mass of Pb(NO₃)₂)*given mass
93.94/310*50.6=15.3
Multiplying the theoretical yield by the percent (and dividing by 100), provides the actual yield.
(theory*%yield)/100=actual yield
(15.3*74.2)/100=11.4

 

Example 2:

For the balanced equation shown below, if the reaction of 57.4 grams of N₂ produces 107 grams of Mg₃N₂, what is the percent yield?
3Mg+N₂=>Mg₃N₂

To answer this question, you use the mass ratio from the balanced equation to determine the theoretical yield.
theoretical yield of Mg₃N₂:(mass of Mg₃N₂)/(mass of N₂)*given mass
100.9/28.01*57.4=207
The percent yield is determined as follows:
(actual/theory)*100=%yield
(107/207)*100=51.5%

 

Example 3:

For the balanced equation shown below, if the reaction of 54.9 grams of C₂H₃O₂Cl produces 32.6 grams of CO₂, what is the percent yield?
4C₂H₃O₂Cl+7O₂=>8CO₂+6H₂O+2Cl₂

To answer this question, you use the mass ratio from the balanced equation to determine the theoretical yield.
theoretical yield of CO₂:(mass of CO₂)/(mass of C₂H₃O₂Cl)*given mass
352.08/378*54.9=51.1
The percent yield is determined as follows:
(actual/theory)*100=%yield
(32.6/51.1)*100=63.8%

Here is  video about the percent yield found on YouTuBe

Volume @ STP

All of the problems in this set are stoichiometry problems with at least one equation participant as a gas at STP. These questions always refer to chemical reaction.So before we calculating,we must write and balance the equation.You will be given an amount of one of the equation to calculate how much another one of the equation.We know:1 mol of gas=22.4 liters at STP.If the question refer to the mass of one of the equation, we must use the formula weight of the material to change from mass to mols.Then we can work out the volume of the gas of that equation.Here is an example.

10 grams of calcium carbonate,CaCO_3,was produced when carbon dioxide was added to lime water (calcium hydroxide in solution). What volume of carbon dioxide at STP was needed?

Given:10 grams of CaCO₃ (the mass of CaCO₃)
Find:the volume of carbon dioxide(in liters at STP)

CO₂   +   Ca(OH)₂     CaCO₃   +   H₂O

Look~we work out the question!

BUT!NOTICE!IT'S At STP only!

Now let's look the map,it's the relationship between mass,moles&volume.

Then you can deal with all this kind of questions,can't you?

Stoichiometry Calculations!

Today, we learned how to do stoichiometry calculations involving particles, moles, and mass. These calculations are somewhat similar to mole conversions except, instead of converting between particles, moles, or mass of just one element in the problem,  you can convert between particles, moles, or mass of more than one element.
*But remember, they are much harder than mole conversioins because you have to use your knowledge of all the mole conversions we've learned in the past, plus what we learned last day about the mole ratio to do these stoichiometry calculations. 

Here is a helpful website with worksheets, pratice questions, and facts about stoichiometry calculations:
http://www.science.uwaterloo.ca/~cchieh/cact/c120/stoichio.html


Remember to use a concept map like this to organize the pathway of your conversions. You don't want to make silly mistakes!!!



^Road map for stoichiometry calculations^

Here is a video example that takes us through each step we must take in order to reach the answer:

 

Stoichiometry

Stoichiometry
a branch of chemistry that deals with the quantitative relationships that exist between the reactants and products in chemical reactions.
In a balanced chemical reaction, the relations among quantities of reactants and products typically form a ratio of whole numbers. For example, in a reaction that forms ammonia (NH3), exactly one molecule of nitrogen (N2) reacts with three molecules of hydrogen (H2) to produce two molecules of NH3:

N2 + 3H2 → 2NH3

A chemical equation is an expression of a chemical process. For example:

AgNO₃(aq) + NaCl(aq) ---> AgCl(s) + NaNO₃(aq) In this equation, AgNO₃ is mixed with NaCl. The equation shows that the reactants (AgNO₃ and NaCl) react through some process (--->) to form the products (AgCl and NaNO₃). Since they undergo a chemical process, they are changed fundamentally.
Often chemical equations are written showing the state that each substance is in. The (s) sign means that the compound is a solid. The (l) sign means the substance is a liquid. The (aq) sign stands for aqueous in water and means the compound is dissolved in water. Finally, the (g) sign means that the compound is a gas.
Coefficients are used in all chemical equations to show the relative amounts of each substance present. This amount can represent either the relative number of molecules, or the relative number of moles (described below). If no coefficient is shown, a one (1) is assumed.

To solve questions as conversions, you need to have conversion factors. Conversion factors relate units to one another. For example, there are 100 cents in 1 dollar, or 100 cents = $1. To use this as a conversion factor, write it as a fraction:

Since 100 cents = 1 dollar, this fraction is equal to 1. That means you can multiply it by anything else, and still have the same quantity that you started with. For example, if you want to convert $5.27 to cents, you can multiply it by the fraction. The dollars cancel out, leaving you with 525 cents:

We can also flip the fraction to get a new conversion factor:

As long as the top and bottom are equal to one another, and we're careful to cancel out units to see what we have left, we can string conversion factors like this together to convert from a starting number to a final answer.

That brings us to stoichiometry. Stoichiometry is the study of relationships in chemical reactions. in other words, it's the study of what amounts of things are equal to amounts of other things in chemical reactions.

Stoichiometry Tutorial website: http://www.chemical-stoichiometry.net/

Endothermic and Exothermic Reactions

We all know that an exothermic reaction gives off energy in the form of heat, light, or sound, and that an endothermic reaction absorbs energy.  If the reaction takes more energy to break the bonds that hold molecules together, it is endothermic. If it takes less energy, the reaction is exothermic.

ENTHALPY, or "H", is the sum of all kinetic and potential energies in a system.  You will see this term used many times.

Change in enthalpy is denoted as 'delta' H.

Exothermic reactions result in a negative enthalpy, or negative "H".  Also, endothermic reactions are characterized by a positive heat flow, or positive "H".

An example of an endothermic reaction is photosynthesis. Plants convert CO2 and water into oxygen and glucose from the energy from the sun.
The general formula of an endothermic reaction is:
A + B + Energy --> AB


The burning of any substance is an example of an exothermic reaction. 
The general form of an exothermic reaction is:
A + B --> AB + Energy


Energy diagrams tell us about the relative rate of a chemical reaction.   They are also called potential energy diagrams or chemical reaction energy reactions.
Here is an energy diagram of a exothermic reaction:

This is an energy diagram of an endothermic reaction:

where: (a) is the activation energy, which is the energy required to initiate a chemical reaction,
(b) is the change between the reactants and products,
and (c) is the change in energy, or enthalpy



  Check out this video! I hope it helps! 

Here is a FUN quiz about exothermic and endothermic that you can do :)http://www.softschools.com/quizzes/science/chemical_reactions/quiz380.html

Chemical Reaction Lab

Today, we did a lab about chemical reactions.

The purpose of the lab is to observe a variety of chemical reactions and to interpret and explain obsevations with balanced chemical equations and classify each reactions asa one of the four main types.

There was a reaction where we added solid copper(II) sulfate pentahydrate to a test tube and heated it over a Bunsen burner. Over time, the copper(II) sulfate pentahydrate changed colors (blue to white)

In this reaction, we took the results of the reaction above and added drops of water to it. The copper (II) sulfate pentahydrate changed from white to blue color.

Basically, there are four types of reactions in this lab: synthesis, decomposition, single replacement and double replacement.

There is an interesting website showing the flash of combustion, if you are interested, click the link:
http://www.pbs.org/wgbh/nova/fireworks/fire.html

Six Types of Reactions

There are 6 types of reactions. They are Synthesis, Decomposition, Single Replacement, Double Replacement, Combustion, and Neutralization.
Synthesis:
Where 2 or more reactants combine together to form 1 product.
It takes this general form:
A+B--->C.

Decomposition:
This is a reaction where one reactant is decomposed into 2 or more products.
The general form is
A---> B+C

Single Replacement:
This one is more tricky! It takes the general form of
A+ BC---> AC +B (if A is a metal) or A+ BC----> B +AC (if A is a non-metal).
The metals switch with each other and non-metals swith with each other. But that's not all we have to worry about..

Double displacement:
This is when the anions and cations of two different molecules switch places, forming two entirely different compounds. These reactions are in the general form:
AB + CD ---> AD + CB

Combustion:
A combustion reaction is when oxygen combines with another compound to form water and carbon dioxide. These reactions are exothermic, meaning they produce heat. An example of this kind of reaction is the burning of napthalene:
C₁₀H₈ + 12 O₂ ---> 10 CO₂ + 4 H₂O

Neutralization:
This is a special kind of double displacement reaction that takes place when an acid and base react with each other. The H⁺ ion in the acid reacts with the OH^- ion in the base, causing the formation of water. Generally, the product of this reaction is some ionic salt and water:
HA + BOH ---> H₂O + BA


***Note***
Remember that the single element on the reactants side must be above the element it switches with on the ACTIVITY SERIES chart. This is because some elements are more reactive than others.
Refer to the following reaction:
1Cu + 2AgNO3  ---> 2Ag + 1Cu(NO3)2
Cu switches with the other metal, Ag. This is a reaction because copper is above silver on the ACTIVITY SERIES chart.


Here is the activity series chart :

This link will lead you to a bunch of online worksheets.  It also provides a lot of information about all the topics we've learned or will be learning in chemistry. Check it out!
http://www.chalkbored.com/lessons/chemistry-11.htm


Net Ionic Equations:
A Net Ionic Equation is a chemical equation for a reaction which lists only those species participating in the reaction.
To write a Net Ionic Reaction, follow these 3 steps:1) Start by simply writing the overall balanced chemical reaction. This is also called the Molecular Equation.

2) Then, you break apart the soluble molecules into the two ions that are formed (one positive and one negative). You will have to use the solubility rules to do this, they can be found online. If something is insoluble, it should not be broken apart. Write the reaction out with all of the separated ions. This is called the Total Ionic Equation.

3) Then, you simplify by canceling things out if they appear on both sides of the reaction, resulting in the Net Ionic Equation.

For example, let look at the reaction of calcium carbonate with hydrochloric acid to form calcium chloride, water, and carbon dioxide:

Molecular Equation:
CaCO_3(s) + 2HCl_(aq) ---> CaCl_2(aq) + H₂O_(l) + CO_2(g)
Total Ionic Equation:
CaCO_3(s) + 2H⁺_(aq) + 2Cl^-_(aq) ---> Ca²⁺_(aq) + 2Cl^-_(aq) + H₂O_(l) + CO_2(g)
Net Ionic Equation:
CaCO_3(s) + 2H⁺_(aq) ---> Ca²⁺_(aq) + H₂O_(l) + CO_2(g)
Notice that the Cl^- was canceled out from the Net Ionic Equation, because it really isn't playing an important part of this reaction. It is just there to balance out the charge because you can't have an ion just by itself -- you must always pair an ion with another one of opposite charge so that the overall charge is zero.

Read more: http://wiki.answers.com/Q/How_do_you_write_a_net_ionic_equation#ixzz1EwvvFFLi


Read more: http://wiki.answers.com/Q/How_do_you_write_a_net_ionic_equation#ixzz1EwvoG0Ua

If you want to practice more, there is a link for the net ionic equation worksheet:
http://www.docstoc.com/docs/6547241/Net-Ionic-Equations-Worksheet




Have a great weekend!!!

Balancing Equations

Here is a game about balancing quations:
http://education.jlab.org/elementbalancing/index
Try it for fun!



Physical States
- (s) – solid
- (l) – liquid
- (g) – gas
- (aq) – aqueous : dissolved in water
Example:
H2(g) is read hydrogen gas

Writing unbalanced equations
- Write correct formulas for reactants and products.
- Include a yield arrow between them.
- Include states when they are known or given.
- Be careful of diatomics (Dr. HOBrFINCl)

Examples
- Solid mercury (II) oxide decomposes to produce liquid mercury and gaseous oxygen.
- Write formulas and check charges
Hg2+O2- Hg + O
- Add states
HgO(s) Hg(l) + O(g)
- Check HOBrFINCl
HgO(s) Hg(l) + O2(g)

Example 2
- Solid carbon reacts with gaseous oxygen to form gaseous carbon dioxide.
C(s) + O2(g) CO2(g)

You try it!
• Solid magnesium metal reacts with liquid water to form solid magnesium hydroxide and hydrogen gas.

- Solid aluminum dichromate decomposes to form solid chromium (II) oxide, gaseous nitrogen, and gaseous water.

- Gaseous ammonia reacts with gaseous oxygen to produce nitrogen monoxide and gaseous water


Balancing Chemical Equations
- Balanced equations have equal numbers of atoms on both sides of the equation.
- Once formulas have been written, the subscripts cannot be changed. This would change the substances formed.
- Balancing is done by adding coefficients, large numbers in front of the reactants or products. 2 H2O = 4 Hydrogen and 2 oxygen atoms.
- Coefficients in balanced equations must always be whole numbers in the lowest ratio possible.

Writing Balanced Equations
Fe(s) + O2(g) Fe2O3(s)
-Start with the most complex molecule and add coefficients.
4Fe(s) + 3O2(g) 2Fe2O3(s)
-Check that the coefficients are in the lowest ratio.

Balancing equations
-Write the unbalanced equation, leave a space in front of each molecule to add a coefficient.
___Fe(s) + ___O2(g) ___Fe2O3(s)
1 Fe 2
2 O 3
-Underneath the arrow, write the elements and the count for the reactant and product sides.
-As coefficients are added, change the count on each side until the numbers on each side are equal.

Chemical Reactions-Translate word equations

How do we balance the equation?

Balancing chemical equations isn't difficult, once you know the way to do it.

Start by finding out how many atoms of each type are on each side of the equation. Some teachers recommend making a little table listing the numbers of each atom for the left hand side and for the right hand side.

Next, look for an element which is in only one chemical on the left and in only one on the right of the equation.

To balance that element, multiply the chemical species on the side which doesn't have enough atoms of that type by the number required to bring it up to the same as the other side. The number is called the coefficient.

BUT

If you have to multiply by, say, 2 1/2, do so, THEN multiply EVERYTHING on each side of the equation by two to get rid of the half.

Now look for the next element or species that is not balanced and do the same thing.

Repeat until you are forced to balance the hydrogen and oxygens.

If there is a complex ion, sometimes called a polyatomic ion, on each side of the equation that has remained intact, then that can often be balanced first, as it is acts as a single species. The ions NO₃^- and CO₃^2- are examples of a complex ion.

A VERY useful rule is to leave balancing oxygen and hydrogen to the last steps as these elements are often in more than one chemical on each side , and it is not always easy to know where to start. Some people also say you should leave any atom or species with a valancy of one one until the end, and also generally leave anything present as an element to the end.

Example 1
Unbalanced equation:- H₂SO₄ + Fe ---> Fe₂(SO₄)₃ + H₂

Balance the SO₄ first (as it is a complex ion and it is in one chemcial species on each side)
3H₂SO₄ + Fe ---> Fe₂(SO₄)₃ + H₂
Now balance the Fe (which is also in one chemical on each side)
3H₂SO₄ + 2Fe ---> Fe₂(SO₄)₃ + H₂
Finally, balance the hydrogen (although it is in one chemical species on each side, it is usually a good idea to leave it until last)
Balanced Equation:- 3H₂SO₄ + 2Fe ---> Fe₂(SO₄)₃ + 3H₂

Example 2
Unbalanced Equation:- Al + O₂ ---> Al₂O₃

We can start with either the Al or the O, but we will start with Al, as we normally leave O to the end. Even though it wouldn't matter where we started in this case.
Put a two in front of the Al on the left
2Al + O₂ ---> Al₂O₃
Put a 1 1/2 in front of the O₂ on the left
2Al + 1 1/2O₂ ---> Al₂O₃
We don't like halves, so multiply everything on BOTH sides by two
4Al + 3O₂ ---> 2Al₂O₃