Enthaply Calculations

There's nothing do with Enthalpy Calculation in this picture... just my feeling under the test.. 

As we knew that, there'll have either absorbing or releasing energy during the reaction, like the equation from below~
CH4+ 2O2 > CO2 + 2H2O + 812kJ 
And now, we can turn it into mole by "ENTHALPY CALCULATION"

The unit of enthalpy calculation will be KJ/mol,  which has shown that  "KJ divided by mol"

As the equation from above, we can tell  "4" different equation from it, as there have 4 different substance in either reactant or product side.

- 812KJ/1 mole of CH4      -812KJ/2 mole of O2      -812KJ/1 mole of CO2      -812KJ/2mole of H2O
The moles of the compouds are determinded by the number of them individualy in the equation
Moreover,  as it's "releasing", which causes a "NEGATIVE" number

I am BACK~

So, Ex 1) How many moles of CH4 are needed to produce 3000KJ?

First, we can write  -3000KJ DOWN,  and multiply the "CH4" equation from below, which is -812KJ/1CH4

-3000KJ x  1CH4 / - 812KJ   (As we want to reduce the KJ, so that we can get the mole)

3.49458128.......  moles of CH4
SIGFIG TIME~~~
There is only 1 sigfig in - 3000,  so     the answer 'll be  "4 mol of CH4"

Moreover, BE CAREFUL THE QUESTION, ESPECIALLY IT MIGHT ASKS FOR "GRAMS"
As we know one more method to turn it into mole, there possibly will have "Mole Converstion" back

Anyway, GOOD LUCK....

Endothermic/ Ecdothermic 16/2

Endothermic: Absobing Energy  (Positive)

Ecdothermic: Releasing Energy  (Negative)



1: Reactants: a substance before reaction

2: Activatied Complex: The highest point that displays the largest potential energy of the reaction

3: Products: A result that after the reaction.

(a)= Activation Energy,  which is the difference between Reactants and Activatied Complex

So basically, if the Products side have higher energy than the Reactants, which means it's "ABSORBING" energy  >>>  Endothermic     (POSITIVE)

If the Products side have lower energy than the Reactants, which means it's "RELEASING" energy>> Exothermic            (NEGATIVE)

Moreover,  we can also calculate it without looking at the graph:

PRODUCTS  -   REACTIANTS  =  POSITIVE / NEGATIVE 

if it's positive, then it'll be Endothermic, if not, Exothermic then : )

An other punishment to our 1/2...

Energy Equation:

CH4 + 2O2 > CO2 + 2H2O + 812kJ   (Remember, kJ"RELEASING energy will be the product side.)

(Exothermic)

P4O10 + energy > P4 + 5O2  ( ABSORBING energy, Endothermic)

Net equation 14/2

Happy Valentine's day



Net Equation has shown that in double replacement reactions, some ions participate in the reaction while other ions do not participate.

Ex.

KCl(aq) + AgNO3(aq)  >  KNO3(aq) + AgCl(s)

Step 1: Divide the NON - INVOLVED  ions (ions that's not participate to form solid) into element

K(aq) + Cl(aq) + Ag(aq) + NO3(aq)  >  K(aq) + NO3(aq) + AgCl(s)

Step 2: Reduce one on each side, just like doing math

Ag(aq) + Cl(aq) > AgCl(s)   << done  NET EQUATION

Activity series, Solubility

If we want to figure out that the Single replacement have reaction or not, we can always look for    the Activity series .



Ex.

Mg + CoCl2 >  MgCl2 + Co        (Reaction, As Mg has higher activity than Co)

Sn   + NiO    >  SnO     + Ni         (No reaction, Although the equation is completed,Sn has lower activity than Ni)

For Double Replacement, we can look for the SOLUBILITY.

Soluble can refer to (aq) (l) ; INsoluble means (s) < solid

As a Double Replacement is usually have (s) < solid as a product,  which means in the right side or product side of the equation, there is usually have at least one (s) or 2 (s), if so, then it'll have reaction.



Type of Reaction (Part 2) + The activity series lab 31/1

Double Replacement: AB + CD > AC + BD (Hints: Just change their partner and be careful the charge!!)

Ca3(PO4)2 + 3H2SO4 > 3CaSO4 + 2H3PO4

FeCl3 + 3NaOH > 3NaCl + Fe(OH)3

Combustion :

Hints : There always have CO2 and H2O as a result

C10H8 + 12O2 > 10CO2 + 4H2O

CH4     + 2O2   > CO2     + 2H2O

Neutralization:

Hints:  Always reacted between Acid (Start with H) and a base ( end with OH-)

And the products will be "Salt"  and water (H2O)

Type of Reaction (Part 1) 27/1

As combining different elements or compounds together, it'll always have a new substance occure as a chemical change. Through this pocess, it's called REACTION.

By determining different type of reaction, we can obtain the finally result by our brain instead of "doing lab"

First: Sybthesis : A+B > C
4H + O2 = H2O
C + O2 = CO2
H + Cl   = HCl

Sec: Decomposition  (Hints, The OPPOSITES way of SYBTHESES)
A > B + C

K2S > K2 + S
2Na2O > 2Na + O2

Third: Single Deplacement:
A + BC > AC + B    (Mental)
A + BC > BA+ C    (Non mental)

Basicly, when one element(MENTAL) and a compound react together, the SINGLE MENTAL element will replace the mental of the COMPOUND.

Following the same format, the way of replacing Non-mental is the same as above

Moreover about Single Replacement:

The less active mental can't replace the other mental which is higher active than it.

To know what's the activity of each mental, we can take a look to our "periodic table" and figure it out