Excess and Limiting Reactants Percent Yield

One reactant is the excess quantity and some of it will be lefy over. The second reactant is used up completely, and is the limiting reactant.

Here's the step to find the excess and limiting reactants:
Step1. Balanced equation
Step2. Convert one to another

and then you can find which one is left over. The one has more is excess reactants and the one that has less is limiting reactants

Here's a video that show an example and clearly explain about excess reactants and limiting reactants:

Percent Yield

Percent yield is the amount of product that is produced during an experiment verse the theoretical amount produced when using stoichiometry. It is simply the amount of product produced divided by the thereotical amount found by using stoichiometry then multiplied by 100% to find the percent.

If you have a theoretical value of 5 grams of water produced but only 3 grams produced when the actual experiment is done you simply divide 3 by 5 and then multiply by 100% to get a 60 percent yield.

The following video is similar to what we explain earlier:

Stoichiometry

Stoichiometry is can be thought of the ratio of moles in a chemical reaction between the reactants and products. The coefficients in a balanced equation tell you the ratios and with this you can find how much of each element or compound is produced theoretically.

For example:

2H2 + O2 -> 2H2O

If you have 10 grams of Hydrogen (H2) you can find out how much water is produced with sufficient amounts of Oxygen.


By simply converting to moles (10 grams of H2 is 10/2 or 5 moles of H2) and then transferring to the other side you will know that you get 5 moles of water and that converted to grams is (5x18=90) 90 grams.

So in one step its:

10 grams of H2 x 1mol/2grams x 2H2O/2H2 x 18 grams / 1mol of 2H2O = 90grams

Here is a video that explain stoichiometry:

Energy Calculations

Energy Calculations

The energy of absorption or release depends on each equation

Exothermic reactions have the energy on the right hand side and a negative H

Endothermic reactions have the energy on the left hand side and a positive H

H is the energy of charge of a reaction and is expressed in JK per mole of the chemicals

CH4+2O2 à CO2+2H2O+812KJ

-812/1mol CH4

-812/2mol O2 (-406)

-812/1mol CO2

-812/2mol 2H2O (-406)

0.45 mol H2O * -812/2mol 2H2O = -190KJ

2500 energy release

 -2500*1mol CH4 / -812 = 3.1mol of CH4

How many gram of O2 would needed to produce 2500KJ of energy?

-2500* 2mol O2/-812 = 6.2 moles of O2

6.2 moles of O2 * 32g/1 mol = 200 of O2

Translating Word Equation/ Naming Compound

Translating Word Equation/ Naming Compound

Ionic Compound

Metal stay the same and non metal has to add “ide” in the end

LiCl à Lithium Chloride

BeS à Beryllium Sulphide

PbF4à Lead(IV) Fluoride

Covalent Compound

We put word in front of non metal for different number

1-      Mono

2-      Di

3-      Tri

4-      Tetra

5-      Penta

6-      Hexa

7-      Hepta

8-      Octa

9-      Nona

10-  Deca

11-  Hendeca

12-  Dodeca

We put everything except mono for the non metal in the front.

Everything for non metal in the back

Acids

HCL          Hydro Chloric acid

H2SO4      Sulphuric acid

H2SO3            Sulphurous acid

Ate à ic

Ite à ous

Lab- 5B

Lab- 5B

Objective:

1. To observe a variety of chemical reaction

2. To interpret and explain observations with balanced chemical equations

                3. To classify each reaction as one of the four main types

Reaction 1:

       

Adjust a burner flame to high heat.

Using crucible tongs, hold a 6cm length of bore copper wire in the hottest part of the flame for a few minutes

Changes during: it starts to change color

Changes after: it turns to black

Equation- Cu+O2 à 2CuO (synthesis)

Reaction 2:

       

Clean an iron nail with a piece of steel wool so the surface of the nail is shiny

Place the nail in a test tube and add copper (II) sulfate solution so that one half of the nail is covered

After approximately 15 mins, remove the nail and note any changes in both the nail and the solution

Changes during: liquid starts to turn green and bubbles all over the nail

Changes after: liquid becomes green

Equation- 3CuSO4 +2Fe à Fe2 (SO4) + 3Cu (single replacement)

Reaction 3:

Put some solid copper (II) sulfate pentahydrate in a test tube so that it is 1/3 full

Using the test tube clamp to hold test tube, heat the test tube, moving it back and forth gently over burner flame

        Continue until there’s no further change is observed

Changes during: smoke appear

Changes after: It turns white

Equation- CuSO4 .5H2Oà CuSO4 +5H2O (decomposition)

Reaction 4:

Allow the test tube contents from reaction 3 to cool

Use medicine dropper to add 2 or 3 drops of water

       

Changes during: change color, heated

Changes after: turns black to blue

Equation- CuSO4 +5H2Oà CuSO4 .5H2O (synthesis)

Reaction 5:

Allow the test tube one quarter with calcium chloride solution. Fill a second test tube one quarter full with sodium carbonate solution

Pour the calcium chloride solution into the test tube containing sodium carbonate solution

       

Changes during: smoke it’s a fast reaction, turn white after added together

Changes after: white solid and becomes milky

Equation- CaCl2 (aq) +Na2CO3 (aq)à 2NaCl2aq) +CaCO3(s) (double replacement)

Reaction 6:

Place a piece of mossy zinc in a test tube

Add hydrochloric acid solution to the test tube until the mossy zinc is completely covered

       

Changes during: zinc starts to get less, bumbles starts to appear

Changes after: zinc disappears, liquid turns a little white

Equation- 2HCl+Znà ZnCl2+H2 (single replacement)

Reaction 6:

Half fill as a test tube with hydrogen peroxide solution.

Add a small amount of manganese (IV) oxide

Test the evolved by placing a glowing splint into the mouth of the test tube

       

Changes during: Bubbles occurs

Changes after: the blowing splints burning again

Equation- 2H2Oà(MnO2) 2H2O+ O2 (decomposition)

Endothermic and Exothermic

Every reaction also has an exchange of energy either endothermic or exothermic. Endothermic means the reaction takes in the energy around it. Exothermic means that energy is realeased by the reaction.


This is a graph of an Endothermic reaction.

This is an Exothermic reaction:

There is a very subtle difference between the two, in the endothermic the product has more energy than the reactants and in the exothermic reaction the product has less energy. Aside from the the same thing happens, enough energy is needed to get the reactant to the activated complex ( the activation energy) and then depending if the reaction is endothermic or exothermic energy is left in the product or given off. The difference of the energy in the product and the reactant is the ∆H  and is positive only if the reaction is endothermic and negative when the reaction is exothermic.

Also when writing up chemical reactions enegry can be included to show how the reaction works.

For example:

AB + 125kJ -> A + B