Used in a sentence: The simplicity of comparing endothermic and exothermic equations caused the groundhog to ululate.
Say what?
Here is some review from previous years:
-All chemical reactions involve changes in energy or heat
-Exothermic reactions GIVE OFF energy
-Endothermic reactions TAKE IN energy
Today, we will be looking at ENERGY DIAGRAMS in depth. These diagrams show the changes the reactants go through as they become products - how much energy they start out with, how much energy they have at their peak, and how much energy they are left with.
With this graph, which looks something like this, we will be able to see whether the reaction is endothermic or exothermic.
-The x-axis of the graph represents the time passed, the y-axis of the graph represents the amount of energy in kJ
-The flat part of the graph (just before the "hill) labeled "Substrate" represents the energy of the reactants. This is how much energy the compounds START with.
-The flat part of the graph (after the "hill") labeled "Product" represents the energy of the products. This is how much energy the compounds END with.
Comparing just these two features will allow you to determine whether it is a endothermic or exothermic reaction, but in order to add this to the chemical equation, we must investigate further.
-The energy of activated complex, labeled transition state on the graph above, is the potential energy of the transition state between the reactants and the products. In other words, it's the highest possible amount of energy the compounds can reach in the reaction process
-The activation energy is the energy that is added to to the reactants to get them to progress. This is found by subtracting the energy of the activated complex by the energy of the reactants.
-Delta H or the change in enthalpy (heat contained in the system) during the reaction. This is found by subtracting the energy of the reactants from the energy of the products.
-A negative H will signify an exothermic reaction - you end up with less energy than you started with
-A positive H will signify an endothermic reaction - you end up with more energy than you started with
Once you find the H, you can use it in equations like this:
Fe + Cl2 = FeCl3 + 432kJ
This means that an exothermic reaction occurred as the product needs 432kJ of energy to equal the reactants (it lost this energy).
In an endothermic reaction, the added energy appears on the reactant side.
You will be asked to draw graphs when given certain information like activation energy, delta H, the amount of energy in the products and the reactants, or you may be given the activated complex instead of activation energy.
A quiz on types of chemical reactions!? Fun stuff.
Don't think you did too well on the quiz? Get confused of what kind of reaction is occurring still? Well here's a quiz for you. Remember the good ol' days from grade 10 science. Yeh, this is just an easy little quiz. Awesome quiz for types of reactions.
What we covered:
1) Translating word equations:
Ex. calcium and chlorine combine to form calcium chloride.
Ca + Cl2 --> CaCl2
2) Balancing equations:
_Mg + _ AlCl3 --> _MgCl2 + _ Al 3Mg+ 2AlCl3 -->3MgCl2 + 2Al
3) Types of reactions:
- Synthesis: A + B --> C
- Decomposition: A--> B+C
- Single Replacement: A+ BC --> AC +B
- Double Replacement: AB+CD --> CB + AD
- Combustion: AB + O2 --> AO + BO
- Neutralization: HA + BOH --> H2O +BA
4) Predicting products, solubility, and net ionic equations.
Now that we've done that, let's take it to another level.
Let's take the same examples and sort them into states. Remember? Aqueous, solid, gas etc?
1) 1AgNO4 + 1KPO4 ----> 1AgPO4 + 1KNO3
Look at the balanced equation and then look at your list of solubility sheet. If you don't have one click on the link below: Solubility Chart
Now look at the highlighted part. First put your finger on Phosphate and slide it across to see if it is a soluble or not a soluble to silver. Do the exact same thing with KNO3.
It will look a little like this : 1AgNO4 + 1KPO4 ---->1AgPO4(s) + 1KNO3(aq) Looking at the balanced equation we need to separate the compounds, the easier way to do this is looking at the solid. If both compounds in the highlighted part is a aqueous that means no reaction occurred. However if one compound is a solid and the other an aqueous then a reaction occurred and the separated compound would look like.... Ag+1(aq) + PO4(aq) ----> AgPO4
**REMEMBER TO WRITE THE CHARGES!!**
Try it with the other ones and see what you come up with!
Today, we completed Lab 5B - Types of Chemical Reactions. We were able to observe synthesis, decomposition, single replacement, and double replacement in action!
First thing's first! SAFETY: ALWAYS MAKE SURE YOU HAVE ON YOUR LAB APRON AND SAFETY GOGGLES. Don't wanna corrode those eyes!
Then you may begin with the reactions... I will sum them up.
Reaction 1: This involves burning copper wire with a bunsen burner. Using crucible tongs, hold the wire over the hottest part of the flame. The copper will begin to change colours.
For those who were unable to observe this in class:
Reaction 2: This involves placing a shiny nail in copper(II)sulphate. This is an example of SINGLE REPLACEMENT, ladies and gentlemen. The magic is that 15 minutes later, the part of the nail that was submerged under the copper(II)sulphate will be coated with copper! Cooooolio :)
Reaction 3: Heating some copper(II)sulphate. Ooohhhhh do I remember heating a HYDRATE from Lab 4C? Kekekeke... So what happens when the water is heated and evaporated?
Reaction 4: What happens when water is added back into the now anhydrous copper(II)sulphate?
Reaction 5: Pour calcium chloride solution into a sodium carbonate solution.
Here is a video, this uses sodium BICARBONATE
Reaction 6: Mossy zinc is covered by hydrochloric acid!
Here is a video if you missed it!
Reaction 7: Manganese(IV)oxide is added to hydrogen peroxide solution. Then, the gas is tested by placing a glowing splint into the mouth of the test tube - the gas should cause the test tube to light up even brighter!
Here is a video, seemingly exaggerated. Because this definitely DID NOT happen in class today.
After you have finished, WASH YOURHANDS! You'd be a fool if you didn't.
Okay, so on wednesday, we had a sub again.. and she gave us a page of notes on the last three chemical reactions:
Double Replacement:
- a reaction between two ionic compounds
Gerneral Formula: AB + CD --> CB + AD
ex: Na2CO3 + CaCO3--> CaCO3 + 2NaCl
Combustion:
- a reaction where buring in air is involved
General Formula: AB + O2 --> AO + BO
ex: C4H8 + 6O2 --> 4CO2 + 4H2O
Neutralization:
- a special double replacement reaction wehre acids react with bases to produce water and an ionic salt
as products
General Formula: HA + BOH --> H2O + BA
ex: 2HBr + Sr(OH)2 --> SRBr2 + 2 H2O
We've learned about balancing equations and different types of reactions. So it's time to put it to some use! This lab focused on metal/metal ion reactions and their reactivity. So starting off with the beakers.
We started with observing the beakers. Inside each beaker were floating atoms. So, then ratio of ions in the solution were equal to the ratio of ions in the formula. Each beaker, has NO3 in it, meaning that the metal ions are the ones that accounts for the change in colour.
While in solution.
Next was experimenting with the different metals and placing it each of the 4 solutions. Different reactions occurred and were recorded. Some didn't have a
After being put in solution.
reaction, and others did. Things like expanding, changing colour, and changes in the solution occurred. Chemical formulas were written and balanced!
Example: Mg + 2AgNO3 --> 2Ag + Mg(NO3)2
After obtaining the information of which changes occurred to which metals and metal ions, we can conclude which has the higher reactivity. This resulted in the reactivity of metals being the opposite of the reactivity of metals.
So with finding the reactivity of a metal and metal ions, we can predict if they can react or not.
Here's a video on a metal reactivity lab! =)
