3.1 Chemical reactions and chemical equations Flashcards
Combination reactions:
* 2 things are combining to typically form one thing
* most common is when you’re combining an elemental metal, w/ an elemental nonmetal
* When you mix a metal and nonmetal you form an ionic compound
* A proper ionic compound has no overall charge
Na(s) + Cl2(g) –> NaCl2
* This is wrong
* Cl is a diatomic which is why were seeing 2 here
* However, NaCl2 has an overall charge of -1, meaning its wrong –> ionic compounds do not have an overall charge
So it should look like this
Na(s) + Cl2(g) –> NaCl
* it will be a 1:1 ratio not a 1:2 ratio
* So you can’t just sandwhich those 2 reactants together and form a product –> have to make sure theres no overall charge
* keys is that charges need to go out to 0
* So now we need to balance it. The Na’s look good because we’ve got 1 on each side, however the Cl isnt correct because we’ve got 2 on the left and only 1 on the R
* So we can’t add any subscripts at this point in the game because it would unbalance the ionic compound (which again must be neutral). The only thing we can do is add coefficents (numbers infront) to balance it
Na(s) + Cl2(g) –> 2NaCl
* So this now balances out the clorines because we’ve got 2 on each side
* Adding the coeffiecnt doubles botht he Na and Cl in the product compound
* However, no the sodiums are unbalanced because we’ve got 1 on the R and 2 on the left
2Na(s) + Cl2(g) –> 2NaCl
* by adding the 2 infront of the sodium we’ve balanced the sodiums (2 on the R 2 on the left)
* Cl is still balanaced (2 on the R 2 on the left)
* and 2NaCl is a neutral ionic compound
* So this is correct
* Key is that everything must be balanced and there needs to be no net charge on the product
Decomposition reaction: Single reactant breaking up into multiple parts - below is decomposition because we have 1 reactant (L) and more than 1 product (R)
CaCO3 (s) –> CaO(s) + CO2(g)
* These are typically called thermal decomposition reactions, meaning they requires heat
* He drew a little triangle over the arrow, representing that heat was used
* this is completely balanced - no coefficents needed
Combustion reaction
* this is like burning something
* can’t combust somethign on the moon because theres no atmosphere on the moon so theres no oxygen on the moon
* so combusion is the reaction of something w/ oxygen gas
* So the way we put a fire is wrapping someone in a blanket –> what you’re really trying to do is starve those combusion reactions of oxygen (because you need oxygen to have combustion reactions)
* typically a hydrocarbon + oxygen
* for a hydrocarbon you’re always going to form CO2 and water
C3H8(g) + O2(g) –> CO2(g) + H2O(l)
* what you want to look for when balancing a pesky equation is an element that only shows up on both sides once, in either 1 element or 1 compound
* Carbon for instance only shows up in 1 reactant and 1 product, that would be a good place to start - hydrogen as well - oxygen would be a bad place to start
* So we’ve already got the whole proper formula, we can’t change any subscripts from here - so we can only modify the subscripts
C3H8 + O2 –> 3CO2 + H2O
* added a 3 infront of the carbon to balance it
* now lets do hydrogen next because it only shows up in one spot on either side (just like carbon)
C3H8 + O2 –> 3CO2 + 4H2O
* added a 4 infront of hydrogen to get 8 on either side
* now were at a point where we can deal with the oxygens
* we have 2 oxygens on the L and 10 on the R
C3H8 + 5O2 –> 3CO2 + 4H2O
* added a 5 infront of oxygen to balance the L with the R
this is now a balanced reaction
* just remember that combustion is a hydrocarbon (hydrogen + carbon) and it reacts w/ O2 (which is why it works on earth and not the moon)
* The products are always going to Be CO2 and water
Double replacement reaction (can also be called double displacement reaction)
* aqueous reaction - takes place in water as a solvent (so they’re dissolved in water)
AgNO3 (aq) + Na2S (aq) –>
* in a double replacement reaction you’re litteraly just going to have cations and anions trading partners
AgNO3 (aq) + Na2S (aq) –> AgS (aq) + Na2NO3 (aq)
* notice the cations and the anions just switched places (both of them did = double)
* cation (+)is always written before the anion (-)
* So now we have to get this formula balanced out to 0 because it is an ionic compound
* Ag = always +1
* NO3 = NO3- (polyatomic)
* Na = +1
* S = -2
read below
By adding a subscript to balance the ionic compound and make it neutral we added an extra silver making the entire equation unbalance, so now we need to balance it
AgNO3 + Na2S –> Ag2S + NaNO3
* so notice the silvers are unbalanced so lets fix it
2AgNO3 + Na2S –> Ag2S + NaNO3
* now we have balanced silvers but the NO3 is unbalanced
AgNO3 + Na2S –> Ag2S + 2NaNO3
* so I’ve fixed the NO3’s but now I have 2Na’s
* However, I’ve got 2 sodiums on both sides (because the Na’s were unbalanced to begin with)
* So this is now a balcned equation
in the next chaper hes going to give us solubility rules which will allow us to predict which state the products will be in after the reaction (liquid, gas, solid etc…)
* soluble = aqueious (its dissolved in the water)
* Insoluble = solid –> it doesnt dissolve in the water
Single replacement reaction (also called single displacement reaction)
* aqueous reaction –> takes palce in water as a solvent (so they’re dissolved in water)
* often a type of oxydation reduction reaction or redox reaction
* in a single reaction, instead of having the cations and anions trading partners, we have whoever is starting off alone (in this case its zinc) replacing somebody in another compound
Zn(s) + CuCl2 (aq) –>
* In this case it would be Zn replacing Cu (because it wants to be a cation w/ an anion becuase its an ionic compound)
Zn(s) + CuCl2 (aq) –> ZnCl + Cu
* So in this case Zn replaced copper to combine w/ Cl
Zn(s) + CuCl2 (aq) –> ZnCl2 + Cu
* added subscript of 2 to clorine because zink is always + 2 and ionic compounds must be neutral
This is now a balanced equation
solute
Substance that dissolves in the solvent
Solvent
The solvent is the substance that dissolves the solute and is typically present in a larger amount than the solute
Example: In a saltwater solution, salt is the solute, and water is the solve
Combustion
Its a hydrocarbon combining w/ O2 –> CO2 and Water
combination
Decompoisition
Its going to make an ionic compound
Al is a transition metal, however, it always carries a +3 charge (one of out special ones)
Start by balancing the ionic compound to make it neutral and then sort out balancing the actual equation by adding coefficient (numbers infront)
just have to know the reactnt must be combined w/ oxygen and the contralateral side must have CO2 and water
this was hard
So you have to first know oxygen gas is O2 (its diatomic) while elemental al is just Al
So its a metal and a nonmetal which forms an ionic compound. Now my job is to balance that
however as a product the oxygen doesnt have to stay as oxygen gas because its combining w/ aluminium - it breaks apart
