Alkenes & Alkynes

    Alkenes and Alkynes have similar naming rule as with Alkanes. Alkenes are hydrocarbons with one or more double bonds. There is one special property by Alkenes, some molecules have same structure but different geometry are called Geometric Isomers. There're mainly 2 types of isomers, cis and trans.

    Alkynes  are hydrocarbons with one or more triple bonds, their general formula is Cn H2n-2, they have similar naming rules to alkenes except they do not have geometric isomers.

Here is a link to show you what Alkenes and Alkynes really are:
http://www.youtube.com/watch?v=7XbYhjyUI-M

Percent Yield

    So today we did some stuff about percent yield. It is a ratio of amount of product obtained to amount of product expect. Let's simplify it, which is the grams of product recovered divided by the grams of product expected from stoichiometry. Then multiply the results by 100%. We also did something called percent purity, it is the ratio of mass of pure substance to mass of impure expressed in a percent. Which is mass of pure substance divided by mass of impure substance and multiply the results by 100%.

http://www.youtube.com/watch?v=TKNxdL7DN1I

Lab 6D

    So today we did a lab which is determining the limiting reactant and percent yield in a precipitation reaction. The objectives are to observe the reaction between solutions of sodium carbonate and calcium chloride; To determine which of the reactants is the limiting reactant and which is the excess reactant; to determine the theoretical mass of precipitate that should form and to compare the actual mass with the theoretical mass of precipitate and calculate the percent yield.

Stoichiometry Exercise

Is 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 withc)  three molecules of hydrogen (H₂) to produce two molecules of NH₃:

N₂ + 3H₂ → 2NH₃

Example 1 : Ca(s) + 2HCl(aq) ----> CaCl2(aq) + H2(g)

a) How many atoms of Ca are needed to produce 1 molecule og Hydrogen?
Ans : Base on the equation : 1 mole of Ca/1 mole of Hydrogen = 1

b) How many moles of HCl are needed to produce 0.452 moles of CaCl2?

Ans : 0.452Ca x 2 moles of HCl/1 mole of Ca = 0.904mol

c) How many grams of Ca will react with 1.05moles of HCl?

Ans : 1.05moles of HCl x 1mole of Ca/2Hcl = 0.525moles of Ca

d) How many grams of CaCl2 will be formed when 2.00g of hydrogen is formed?

Ans : 2.00g/2 moles of H2 x 1 mole of CaCl2/1 mole of H x (40.1 + 35.5 x 2)g = 111.1gCaCl2

e) How many moles of of HCl are needed to form 6.12grams of CaCl2?

Ans : 6.12g of CaCl2/(40.1 + 35.5 x 2)mol of CaCl2 x 2 moles of HCl/1 mole of CaCl2 = 0.11 mol of HCl

Chapter 6 - Stoichiometry

  
As the definition above, Stoichiometry deals with quantitative analysis of chemical reactions, it is also the relationship between reactants used and products produced. It can use as molecules AND moles; it can also be used as conversion factors. The coefficient in balanced equations tell us the number of moles reacted or produced.

Stoichiometry calculations can predict how elements and components diluted in a standard solution react in experimental conditions. Stoichiometry is founded on the law of conservation of mass: the mass of the reactants equals the mass of the products.

A stoichiometric amount or stoichiometric ratio of a reagent is the amount or ratio where, assuming that the reaction proceeds to completion:

1. all reagent is consumed,
2. there is no shortfall of reagent, and
3. no residues remain.

Here is a little video that i found on youtube that could help you understand more about Stoichiometry - http://www.youtube.com/watch?v=rESzyhPOJ7I

Exothermic And Endothermic Reaction

An exothermic reaction is a chemical reaction that              

releases energy in the form of heat.

Expressed in a chemical equation:

reactants → products + energy

For an exothermic reaction, this gives a negative value for ΔH, since a larger value (the energy released in the reaction) is subtracted from a smaller value (the energy used for the reaction). For example, when hydrogen burns:

2H₂ + O₂ → 2H₂O

H = −483.6 kJ/mol of O₂                                                                                                      

Examples of exothermic reactions

• Combustion reactions of fuels
• Neutralization reactions such as direct reaction of acid and base
• Adding concentrated acid to water
• Burning of a substance
• Adding water to anhydrous copper(II) sulfate
• The thermitereaction
• Reactions taking place in a self-heating can based on lime and aluminum
• The setting of cementand concrete
• Many corrosion reactions such as oxidation of metals
• Most polymerisation reactions
• The Haber-Bosch process of ammonia production

                                                                                                              

An endothermic reaction is a chemical reaction that          

absorbs in the form of heat.

Expressed in a chemical equation:

reactants + energy → products

 For an endothermic reaction,   this gives a positive value for ΔH, since a larger value (the energy absorbed in the reaction) is subtracted from a smaller value (the energy used for the reaction).

Some examples of endothermic processes are:^[2]

• A chemical cold pack consisting primarily of ammonium nitrate and water.
• Evaporation of water
• Photosynthesis

 

Enthalpy Calculations

So today we did some notes on enthalpy calculations. It is  a measure of the total energy of a thermodynamics system. It includes the internal energy. Which is the energy required to create a system, and the amount of energy required to make room for it by displacing its environment and establishing its volume and pressure. Delta H is the energy change in the reaction in the kJ/mole. The enthalpy of a system is defined as: H= U + pV

This is a video that will help u understand how to calculate Delta H in some enthalpy problems: http://www.youtube.com/watch?v=NoRg7eGfb9k