Chemical reactions tutorial Let’s get started!!

Goals In this tutorial, you will learn… How to recognize 3 of the 5 types of reactions Predict the products of reactions when only given the reactants

What are the 5 types of reactions? Synthesis Decomposition Combustion Single replacement Double replacement

Which 3 will be we learning about?? Synthesis Decomposition Combustion

SYNTHESIS

AB A + B  ONE PRODUCT!! Synthesis Two or more reactants combine to form… ONE PRODUCT!! AB A + B 

Two reactants form one product Synthesis Continued 2 2 Mg + O2  MgO Two reactants form one product BUT WAIT!! Don’t forget about everything you have already learned! Is your equation balanced??

Predicting products Before we keep going… lets learn a few things about predicting products

Predicting products Here are a few important things to remember when predicting products: The compounds form must be neutral ionic compounds (which means you’ll be paying attention to their charges) You do NOT carry subscripts from the reactants to the products. You always balance your equation LAST

Let’s go back to that synthesis example Remember the reaction: Mg + O2  Helpful hint for later…why is oxygen O2 and not just O? Click to find out why

Why O2?? Oxygen is a diatomic molecule, which means when oxygen is by itself it must be O2. Remember that this DOES NOT mean that oxygen is O2 in compounds, only by itself! What are the other diatomic elements? (hint: remember the heavenly 7! F2 H2 Br2 N2 I2 Cl2 O2 Go back

Now to predict the products… Mg + O2  Remember A + B  AB so Mg + O2 will make a compound with magnesium and oxygen. What does a compound with magnesium and oxygen look like??

A compound with magnesium and oxygen… Magnesium is a metal, oxygen is a nonmetal so we must be forming an IONIC compound. What’s the charge of Mg? What’s the charge of O? O 2- Mg 2+

So what’s the compound? Mg2+ O2- Pick… MgO2 MgO Mg2O2

Nope! MgO2 +2 + 2(-2) DOES NOT EQUAL ZERO Try again!

Nope! Mg2O2 2(+2) + 2(-2) = 0 But remember ionic compounds need to be in the simplest form Try again!

Mg + O2  MgO 2Mg + O2  2MgO Yes! Very good! MgO is a neutral, correct ionic compound so our formula is Mg + O2  MgO Finally, balance the equation to satisfy the law of conservation of mass… 2Mg + O2  2MgO

So remember… When predicting products: Make correct ionic compounds THEN balance Let’s move on to the rest of the reaction types…

Decomposition

Decomposition ONE REACTANT… forms two or more products A + B AB 

Decomposition Continued The electrolysis of water is when water decomposes into hydrogen and oxygen gas as shown below: 2H2O  2H2 + O2

Predicting products and decomposition Lets use that same reaction. What if we were not already given the products, how would we predict them? H2O  ?? Water is made of hydrogen and oxygen, so will my products just be H and O?

But wait….something is still missing…. No! Remember, H and O are both diatomic elements. H2O  H2 + O2 But wait….something is still missing….

Balance! Don’t forget to balance your equation after you make your products! Your final answer should look like this: 2H2O  2H2 + O2

You try one… What is the correct reaction for the decomposition of sodium chloride, NaCl? NaCl  Na + Cl 2NaCl  Na2 + Cl2 2NaCl  2Na + Cl2

Nope! NaCl  Na + Cl Don’t forget that chlorine is a diatomic element, so it must be Cl2 Try again!

Nope! 2NaCl  Na2 + Cl2 Although this reaction is correctly balanced, sodium is NOT a diatomic element Try again!

Yes! Very good! 2NaCl  2Na + Cl2 This is a correct reaction for the decomposition of sodium chloride. Ready for the last type of reaction?

Combustion

Hydrocarbon?? What’s that?? Click to find out! Combustion Combustion is the burning of hydrocarbons. Hydrocarbon?? What’s that?? Click to find out! When a hydrocarbon reacts with oxygen (O2), the products are ALWAYS….. Yes, ALWAYS… Carbon dioxide and water CO2 + H2O

Hydrocarbons A hydrocarbon is an organic molecule made up of hydrogen and carbon. Remember when we learned about these when we talked about organic chemistry?? C20H42 CH4 C6H10

Balance this equation… Combustion Cont… Since the products of a combustion reaction are always CO2 and H2O, the hardest part about combustion reactions is balancing them CH4 + O2  CO2 + H2O Balance this equation…

CH4 + O2  CO2 + 2H2O Combustion Cont. 4C3H9 + 21O2  12CO2 + 18H2O Be aware… this reaction was pretty easy to balance, some of the combustion reactions get pretty complicated! Like this one… 4C3H9 + 21O2  12CO2 + 18H2O

Not quite, review the types of reactions with me… Ready for your quiz?? Yes! Not quite, review the types of reactions with me…

Ok, now I’m ready for the quiz! Review Synthesis reactions: two or more reactants combine to form ONE product A + B  AB Decomposition reactions: ONE reactant breaks down into two or more products AB  A + B Combustion reactions: a hydrocarbon reacts with oxygen to produce carbon dioxide and water. Hydrocarbon + O2  CO2 + H2O Ok, now I’m ready for the quiz!

Quiz Question 1/5 Which of the following is a decomposition reaction? 2Fe + O2  2FeO Na + AgCl  Ag + NaCl Na2S  2Na + S

Nope! 2Fe + O2  2FeO This is two reactants forming ONE product which is an example of a synthesis reaction Try again!

Nope! Na + AgCl  Ag + NaCl This reaction does not just form one product. This reaction is an example of a single replacement reaction which we will learn about later. Try again!

Yes! Very good! Na2S  2Na + S This reaction is ONE reactant breaking down into two or more products, which is an example of a decomposition reaction. Back to the question! Next question!

Quiz Question 2/5 How can you recognize a combustion reaction? A combustion reaction is the only reaction always has at least two reactants and two products. One of the reactants is always oxygen gas. A combustion reaction always has a hydrocarbon reacting with oxygen to produce carbon dioxide and water. A combustion reaction always has a hydrocarbon reacting with nitrogen, which is a very explosive reaction.

Nope! A combustion reaction is the only reaction always has at least two reactants and two products. One of the reactants is always oxygen gas. We will learn about other reactions that can have more than one product and more than one reactant. This is NOT the way to identify a combustion reaction. Try again!

Nope! A combustion reaction always has a hydrocarbon reacting with nitrogen, which is a very explosive reaction. Although combustion reactions are typically explosive, it is not because they react with nitrogen. Try again!

Yes! Very good! This is how we identify a combustion reaction A combustion reaction always has a hydrocarbon reacting with oxygen to produce carbon dioxide and water. This is how we identify a combustion reaction Back to the question! Next question!

Quiz Question 3/5 Pick correct bubble that finishes the reaction below. K + Cl2  ?? K + Cl2  KCl 2K + Cl2  2KCl K + Cl2  KCl2

Nope! K + Cl2  KCl2 Remember to not carry subscripts over to your products. K has a +1 charge and Cl has a -1 charge so the product of KCl2 is not neutral and cannot be correct. Try again!

Almost! But not quite… K + Cl2  KCl Although this product is correct, the equation is not balanced! Try again!

Yes! Very good! 2K + Cl2  2KCl The products are correct and the reaction is balanced! Great job! Back to the question! Next question!

Quiz Question 4/5 Pick correct rectangle that finishes the reaction below. C2H8 + O2  ?? C2H8 + O2 CO2 + H2O C2H8 + 4O2 2CO2 + 4H2O C2H8 + O2 C2H8O2

Almost, but not quite… C2H8 + O2 CO2 + H2O Great job predicting the products, but…. don’t forget to balance!! Try again!

Nope! C2H8 + O2 C2H8O2 Remember that combustion reactions always have carbon dioxide and water as products Try again!

Yes! Very good! C2H8 + 4O2 2CO2 + 4H2O Products are correct and the equation is correctly balanced. Great job! Back to the question! Next question!

Quiz Question 5/5 Pick correct rectangle that finishes the reaction below. Al + N2  ?? Al + N2  AlN2 3Al + N2  Al3N2 2Al + N2  2AlN

Nope! Al + N2  AlN2 Remember we do not carry over subscripts. Aluminum has a +3 charge and nitrogen has a -3 charge so a formula of AlN2 is not a neutral compound Try again!

Nope! 3Al + N2  Al3N2 Although this equation is balanced, since aluminum has a +3 charge and nitrogen has a -3 charge, this is not a neutral compound Try again!

Yes! Very good! 2Al + N2  2AlN A correct neutral compound for the product and a balanced equation. Great! Back to the question! Finish!

Congratulations! You have finished the chemical reactions tutorial Go back to the start