Energy Diagrams Cont:

The main point is to look at the diagram and to find the potential energy with quick simple calculations. You also have to determine whether it’s endothermic or exothermic.

Potential energy: added energy to create reaction whether released or absorbed.

Terms:

If you look to the diagrams in the previous blogs, you can find all the terms mentioned below. These terms will explain further of what happens in the diagram and what happens to the energy as the reaction proceeds.

·         Energy of Reactants (or just ‘reactants’ on the diagram): the ‘starting’ amount of energy of the diagram

·         Energy of Products (or just ‘products’ on the diagram): The result of the final product of the reaction with the given amount of energy.

·         ∆H: the change in potential energy (or enthalpy) it is given when to calculate the energy of products minus the energy of the reactant (Hprod – Hreact). It is switch to addition if trying to find the Hprod or Hreact out of the ∆H.

·         Energy of the Activated Complex: the transition of potential energy through reactants a products. To find it you must add the activation energy to the reactant.

·         Activation Energy: a ‘must-be’ added energy to continued reaction process. To find it you must minus the activated complex with the reactant.

*A thing about the diagrams, you can tell if the diagram is endothermic or exothermic by simply noticing where the Products line ends up; if it is higher than the Reactants line it is endothermic and vice-versa.*

Now On To Energy Calculations!

The energy is represented in KJ per mole in the chemical equation, and yes you heard it right, the MOLES are back. Which means it is added to the chart of mole equations, and how do you do that exactly? Well by:          (∆H) KJ                        1mol of (chosen element)

                                               1mol of (chosen element)                  (∆H) KJ         

*note: ∆H is not a constant number like in most mole equations so expect different amounts of energy in the reactions.*

-depending on where the ∆H is placed in the reaction, you can tell whether it is endothermic or exothermic, for example:               4C(s) + 6H(g) + O2(g)  à 2C2H5OH(l) + 470 KJ

Because the 470KJ is placed on the right side of the reaction it is exothermic, if on the other side it is endothermic. Let’s use this example again to show how the mole equation works: Calculate the amount of energy released when 1.50 moles of carbon is reacted:                                                   

4C(s) + 6H(g) + O2(g)  à 2C2H5OH(l) + 470 KJ

1.50 mole C x        470KJ     =  176.25 KJ energy released

                            4mol of C

*note: that you must always say ‘Energy Released’ as your final answer, also if the number is negative, by saying that; it gets rid of it for you, lessening confusion.*

-some equations can get a bit complex by asking for grams or molecules, but it should be no different from previous uses of mole equations, they are set up the same way so there should be no difficulty as we have already done them.

Translating Equations

Translating equations just basically means converting a formula to a word equationa and vice versa. 
Let's review.

Step 1: write the formula of the reactants and the products.
silver nitrate + potassium chromate --> silver chromate + potassium nitrate

  +  
AgNO3 + K2CrO4 --> Ag2CrO4 + KNO3

Step 2: balance the equation.
2AgNO3 + 1K2CrO4 --> 1Ag2CrO4 + 2KNO3

Step 3: write in the states.
2AgNO3(aq) + 1K2CrO4(aq) --> 1Ag2CrO4(s) + 2KNO3(aq)

Step 4: add all other values if neccessary(enthalpy)
Complete ionic equation:
-all the reactants and all the products
Take this example:
Ba(NO₃)₂ + CuSO₄ BaSO₄ + Cu(NO₃)₂
the complete ionic equation is
Ba²⁺ + 2 NO₃^- + Cu²⁺ + SO₄^2- BaSO₄ + Cu²⁺ + 2 NO₃<sup>-
Often however, you won't have to write this all out.
Net ionic equation
-only looks at the elements forming a solid.2Na1+_(aq) + SO₄2-_(aq) + Ba2+_(aq) + 2Cl1-_(aq) -----> 2Na1+_(aq) + 2Cl1-_(aq) + BaSO_4(s)
- we can all agree that this is the complete ionic formula, but what is the net ionic formula?
Ba2+_(aq) + SO42-_(aq) -----> BaSO_4(s)</sup>

^{Try several of these problems! List the type of reaction and write a net ionic equation for each.}

1)         ____ NaBr + ____ Ca(OH)₂ à

2)           ____ NH₃+ ____ H₂SO₄ à

3)           ____ Pb + ____ H₃PO₄ à

4)           ____ Li₃N + ____ NH₄NO₃ à

^{The optimist sees the glass half full.
The pessimist sees the glass half empty.
The chemist see the glass completely full, half in the liquid state and half in the vapor state.}

---

Reactions in Real Life- Lab 5B

It's easy to find products of reactions on paper, but it's much more difficult to identify substances when doing experiments.  This is why learning to balance equations is so important!

These are some of the things to keep in mind:

Indicators of chemical changes:

colour change

-hydrate loses water molecules and becomes an anhydrous salt

bubbles
-bubbles rise to the surface as gases are released

heat or light

-as you can see there is steam and condensation on the sides of the test tube, signalling that the reaction released heat

formation of a precipitate

-a solid forms and settles on the bottom of the test tube

Some reactions like combustion react with the elements in air or water.  There are several ways of testing the identity of the substance.  If it is a gas, you could light a splint and put it into the test tube to see if it ignites.  You could also find the mass of 1 mole of the substance( 1 mole = 22.4 L at STP)

Watch these video.

http://www.youtube.com/watch?v=0y9NOyTgJ88&feature=related

Write a balanced chemical equation for the reaction.

What did the person do to confirm the identity of the gas being released?(O2)

http://www.youtube.com/watch?v=mtjbg6ZF5K4

The two reactants are hydrogen peroxide(H2O2) and potassium iodide.  Predict the two products. 
What type of reaction is this?

What evidence is there that a chemical change has occurred?

Endothermic and Exothermic Reactions

• chemical reactions that involve a change in energy
• held together by chemical bonds
• bonds are broken by adding energy
• energy is needed to have bonds join together

2 types: endothermic and exothermic

endothermic:

• absorbs energy 

exothermic:

• releases energy

Enthalpy H is H product - H reactant. It is the heat contained in the system.

Energy Diagrams:

• Activation energy is the energy needed to be added in order for the reaction to progress.
• Delta H is the change in enthalpy: energy of products - energy of reactants.

We all know that elements and compounds undergo reactions. In chemistry there are 6 main types of reactions. They are:

• Synthesis
• Decomposition
• Single Replacement
• Double Replacement
• Combustion
• Neutralization

Wow! It seems like it would be a lot to memorize, eh? Well, actually, it's pretty simple! Here's a breakdown of each reaction and a helpful diagram to help you remember!

Synthesis

-A combination of 2+ reactants into a single product. Think of it as a girl and a boy begin dating.
-General form: A + B --> AB

Ex. 2Na + Cl₂ --> 2NaCl
  
Decomposition

-A break down of a single compound into compounds or elements. Think of it as a the girl and the boy breaking up.
-General form: AB --> A + B

Ex. 2HgO --> 2Hg + O₂

Single Replacement

-An element replaces an ion in an ionic compound. Metal elements switch places with cations, which are the positive ions. Non-metals switch places with anions, which are the negative ions. Think of it as a woman stealing another woman's husband! Oh no!
-General forms: AB + C --> AC + B                                         A + BC --> AC + B
                 -this form applies when B & C are anions (-)         -this form applies when A & B are cations (+)

Ex. (metals) 2K + 1CaBr₂ --> 2KBr + 1Ca
    (non-metals) 2BeCl₂ + F₂ --> 2BeF + 2Cl₂

There's one more little rule you need to know about single replacement. Cations cannot replace cations willy nilly, and the same goes for anions. You must look at an activity series sheet to make sure that the replacement can take place.

 

As you can see on the activity series to the left, the elements fall in order. If the element that is doing the replacing is higher up than the element being replaced, the reaction will take place. If the element doing the replacing is lower than the element being replaced, the reaction will not take place.

Ex. 2Na + CaCl₂ --> 2NaCl + 1Ca

              = NO REACTION

You see how in the above reaction, the Na (replacer) is lower than Ca (replacee)? That means the reaction does not occur.

Double Replacement

-Occurs when two ionic compounds switch there cations (positive ions). Think of it as two couples switching their partners!
-General form: AB + CD --> CB + AD
Ex. Cs₂CO₃ + BeCl₂ --> 2CsCl₂ + BeCO₃

Similar to single replacement, there is a rule which must apply to the reaction for the reaction to occur. If a change in state occurs in the reaction, then the reaction will occur (usually a precipitate will form). We can find if there's a change in state by using a solubility sheet.



If the compound is soluble, then no reaction occurs. If the compound is not or low soluble the reaction occurs!

• soluble = bad
• non/low soluble = good

Ex.  2NH₄NO₃(aq) + 1BeBr₂(aq) --> 2(NH₄)Br(aq) + 1Be(NO₃)₂(aq)

You see how in the above example, all the products are aqueous? That means no solid has formed, which means there was no change of state that occurred, therefore there was NO REACTION.

Ex. 2NH₄Cl(aq) + Pb(NO₃)₂(aq) --> 2NH₄NO₃(aq) + PbCl₂(s)

Aha! We have an solid that has formed! That means the reaction has occurred!
Now that we know that reaction took place, we should write a net equation. This is how:

• First step is to write out each ion out seperately. Don't forget to write its charge, its quantity, and its state! The solid solution stays as a whole.

2NH₄⁺_(aq) + 2Cl_2(aq) + Pb^2-_(aq)+ 2NO₃^-_(aq) --> 2NH₄⁺_(aq) + 2NO₃^-_(aq) +  PbCl_2(S)

• Next step is to cross out the same ions that appear twice on the reactants and products side

2NH₄⁺_(aq) + 2Cl_2(aq) + 1Pb^2-_(aq)+ 2NO₃^-_(aq) --> 2NH₄⁺_(aq) + 2NO₃^-_(aq) +  1PbCl_2(S)

• Now that all the duplicates are crossed out, we see what's left. Then we make an equation out if them!

                                                       1Pb^2-_(aq)+ 2Cl_2(aq)--> 1PbCl_2(S)

                                                    And voila! There is our net equation!

Combustion

-When burning in air occurs. Reactants are burned and react with the oxygen in the air.The products are oxygen atoms that are usually combined with other atoms.
-General form: AB + O --> AO = BO

Ex. CH₄ + 2O₂ --> CO₂ + 2H₂O

Neutralization

-similar to double replacement, except the reactants, an acid and base, react and produce an ionic salt and water (H₂O)
Ex.1H₂SO₄ + 1Ba(OH)₂ --> 1BaSO₄ + 2H₂O

So we've covered the basics of the 6 types of reactions! Now you should try applying it to equations! These are great website to check out:
http://www.sciencebugz.com/chemistry/chprbbaleq.html

http://www.youtube.com/watch?v=ul4xRy8hcsQ

Balancing Equations Quick Review

Remember in grade 10 how we all learned how to balance equations? No? Don't remember? Well, don't worry, you've come to the right place! Here's a review on how to balance equations.

The whole purpose of balancing equations is to get the atoms on both the products and reactants side to be equal. There are no exact steps to balancing equations. Practice, practice, practice! That is the way to getting the feel of balancing equations; it makes it a lot easier once you've practiced a lot. However, there are certain rules that can help make balancing equations easier:

                     Let's use the following example as a guide

                   Original: 1NaCl + 1Li₃PO₄ --> 1Na₃PO₄ + 1LiCl

                 Balanced: 3NaCl + 1Li₃PO₄ --> 1Na₃PO₄ + 3LiCl

• Balance polyatomic compounds as whole, not seperately (Ex. PO₄ -- balance this as PO₄, not as P and O₄)
• Balance each section as you go along (Ex. when you first encounter the Na3 on the products side, go back to the NaCl on the reactants side and add a 3, leaving you with 3NaCl. Now that you have 3 Cl, go back to the products side and add a 3 infront of LiCl, making it 3LiCl)
• Leave single elements last. These will be the easiest ones to balance because single elements (Ex. O₂, Al, Ba)

**When your finished balancing your equation, and some elements/compounds don't have a coefficient infront of it, always put a 1**

Examples

__CaC₂ + __O₂ --> __Ca + __CO₂

__Mg(OH)₂ + __Ag --> __AgOH + __Mg

__AlP + __BeF₂ --> __AlF₃ + __Be₃P₂

Answers:

1CaC₂+ 1O₂ --> 1Ca + 1CO₂

1Mg(OH)₂ + 2Ag --> 2AgOH + 1Mg

2AlP + 3BeF2 --> 2AlF₃ + 1Be₃P₂                    

More practice? Try these awesome sites!

http://www.sciencegeek.net/Chemistry/taters/EquationBalancing.htm

http://www.chemistry-drills.com/balance.php?rxn_drill=balance_easy