Balancing Equations and Types of Reactions

[00:00:00]so in the third of these videos for the introduction to chemistry we're going to look at balancing equations so kind of calculation is going to show us what happens reactants have been converted to products they're irreversible changes often so we can't go back we do occasionally get reversible reactions that we'll have a look at later at GCC probably came across word equations a lot copper and oxygen make copper oxides copper and oxygen are the reactants copper to oxide is the product we do not write word equations everything is always a symbol equation so we need to be able to convert word equations into symbol equations and they must always be balanced equations you cannot just write the symbols and leave it to must always balance your equations so they're gonna give us the symbols and formulas and they're going to balance for atoms the first thing we can do is replace the words in our equation with the correct formula so we're looking back at our previous word from earlier on I'm saying what's the correct formula for copper so first thing you need to ask yourself is is copper one of those elements that just goes round or Cu copper that's its symbol or is it one of the diatomic elements well copper is not one of the diatomic elements so we just write Cu for its formula it's a cactus see in a little you just as it is on the periodic table oxygen is one of our diatomic element so it goes round in pairs o2 and then copper oxide formulas that we've just been looking at an ionic formula so copper to Cu 2 plus oxide group 602 - putting together the formula of copper to oxide is see you owe two pluses and two minuses balance see you owe we're in the correct formula down now we can adjust the numbers of these formulae without changing their formula cannot change these formula in any way so no marsuits subscripts now only big numbers in front only stoichiometry that's a fancy word for balancing the amounts so we can only change the big numbers in front so we have to make them to eat along both sides now there's a lots of ways that you can do this and you just need to work your way through I'm going to check my metal there's one copper on each side and then I'm gonna check the oxygens but there's two oxygens on the left so if I were to just copy that down for a second now I'm going to start putting some numbers in front plus two oxygens in or two I need to have two oxygens on this side and the way to do that is have two copper oxides which then means I've got two coppers so I need to go back and put a two in front of copper and a double check was to see use and two errs on each side is a balanced chemical equation and I haven't changed any of the formulae that I've worked out you can then add some state symbols and this you only need to do this if the exam board asked you to do this I wouldn't do this if I wasn't asked but we know that copper was one of our solid elements oxygen is a gaseous element and copper ii oxide is a solid at this stage we wouldn't necessarily expect you to know that so have a go at balancing these three I'm gonna pause the video and allow you to have a go and then when you come back and then you unpause the video the answers should be there there you go I've had to go at balancing those equations and I've put in the numbers these are a little bit more difficult because we're turning the city the words into symbols and balancing so I'll go through the first one with you got magnesium which I know is energy oxygen which I know is o2 and magnesium oxide which we can work out we know that my museum is an mg 2 plus course in group 2 and oxide is over 2 minus so it's gonna be mg and then I can go and put my balancing numbers in again I'm gonna pause the video see if you can come up with the formulas of all of these now you might have to flick back through your pack and remind yourself of how to come up with the formulas but see if you can call the formulas and balance these equations my knees one was very similar to the example from copper earlier on hydrochloric acid is here at CL I've worked out the formula sodium carbonate using the ions and sodium chloride and I remembered the formula of carbon dioxide in water now a little trick that you might want to learn to balance equations that include assets and this if you remember the words macho there's a little order that you can do things if you balanced the metal first and then once you've followed the metal you can balance any other actives some people might say the absurd here I say any there isn't carbon-hydrogen sorry I went to the metal fair so there was two na s so I put two na s on this side then I go for anything that isn't carbon hydrogen oxygen in this case that's the CL so to balance the CL now that there's two CLS over here there needs to be two CLS over here and then I checked the carbon one C one C and then the hydrogen's two H's to here chest and then the oxygens three oxygens to three oxygens so again because this is a reaction with an acid we can use this again oh it's the metal there was two lithium's on the right so I needed two lithium's on the left there any other is a salt fat one on each side there's no carbons the hydrogens balance is two on each side and the oxygens as far on each side okay we're gonna move on from and balancing but we're gonna continue balancing by looking at just some of the words we use for different types of reactions in a little chemistry so the first one being combustion and by combustion we mean burning in oxygen reacting it with oxygen so a meteor and it's one of the ones you've had to memorize makes carbon dioxide and if we use that matchy rule we don't have a metal or anything other than carbon hydrogen oxygen so we're just gonna do the Chur part one carbon one carbon four hydrogens we'll need two waters to make four hydrogen's on the right there's two options on the right and another two oxygens in carbon dioxide so2 in the water and two in the cabinet's as far together so we'll need two oxygens the second type of reaction that you might hear about is called decomposition sometimes people confuse combustion and decomposition decomposition is when you heat it up but you don't react it with oxygen you just break it down you don't react it so we was taking the one thing and breaking it down so pause video see if you can fill in reformulate and balance the equation there we go it balances once you've put the formula you can see that it balances next one is a neutralization so acid and alkali or acid embeds to form water so again pause the video have a go and come back and see whether you've got it right hopefully if you this correct you should have got that sodium hydroxide NaOH position or three mix nano3 sodium nitrate and water so redox reactions reduction and oxidation combined again yay love come across these are deucesy although you might have called them displacement reactions there's two here for you to have a go up again using all the rules for creating formula and then balancing equation see if you can write equations for these two plots - they're my Museum in hydrochloric acid maximum using fluoride and hydrogen and chlorine and potassium bromide makes bromine and potassium chloride Bush tip burning in oxygen decomposition eating to break it down neutralization acid and alkali reacting together to make water and redox reduction and oxidation taking place together one element is losing electrons another is gaining so now our top example here magnesium is losing electrons to become magnesium ions and the hydrogen ions in the acid I'm gaining electrons to become hydrogen gas so - I am say H plus have no electrons when in hydrogen gas there's a shared pair so there are two electrons in there and hate to and here we've got chlorine gaining electrons to become chloride ions and bromide ions losing electrons to become bromine these are redox reactions other words that you might come across are EXO an endothermic EXO meaning heat out the exit is the way out and sperm is the heat so we're gonna release heat to the surroundings which reactions give out heat well any kind of burning wood so carbon and oxygen carbon burning an oxygen to make carbon dioxide balances it is an endothermic reaction whose any reaction that takes heat in from the surroundings it's quite often you after you use a Bunsen burner or a source of heat to make these work hydrogen iodide h i hydrogen is diatomic as is iodine to balance that I was new to hydrogen iodide so different types of reaction and then words to describe the energy involved in reactions EXO an endothermic cumin is another word reactions that are reversible we see this error here and we sorrow here representing that the reaction the reactants can form the products but the products can be reverted into the reactants ilysm can happen in either direction and all three things will be present at any one time so salt for dioxide oxygen sulfur trioxide and then we need to balance that now to make the oxygens balance given that that's a three and this is a two and two that's four we're gonna have to try to make three become an even number put two in front of that it's gonna give me six I have now need two sofas and I've got six oxygens on each side you can this is just a little point some of you might prefer to do this balance it in a different way this is just something extra another way to balance it if there was two oxygens and two more and we're gonna needed three half a mole of oxygen gas there then that would be intuitive three options on the left and serious I'll say we can't have half oh no - isn't that just an a no we're not talking about half of one we're talking about half of one mole and one mole is millions and trillions of them so we can have a half in our balanced equations if we like we learn lots more about reversible reactions later in the course