IGCSE CHEMISTRY CONSTRUCTION OF CHEMICAL EQUATIONS

welcome to igcs chemistry lessons in this video we are looking at constructing chemical equations in introduction let us introduce what a an equation is an equation is a chemical sentence which describes what is happening in a chemical reaction therefore by the end of this lesson you will be able to construct word equations and turn these word equations into equations using symbols General features of chemical equations chemical equations are generally composed of number one the reactants which are normally written at the left hand side of a chemical equation number two to the products which are normally written at the right hand side of a chemical equation the plus sign on the left hand side which means react with there is also a plus sign on the right hand side which means and so please take note there is a plus sign when the plus sign is on the left side of the equation it is going to mean uh it is going to mean react with when the S Plus is on the right hand side of the equation it is going to mean and now someone might be wondering what the left hand side is and the right hand side is in a short while we're going to see this so we are saying the equation also has an arrow so the arrow between the reactants and the products means to form or to produce okay to form or to produce let's look at the first example we can have an equation where we are saying A + B = C + D so this side here we have what we call the reactants then this side here we have what we call the products so this Arrow here is the one that is dividing the equation into two sides we have the left hand side okay and the right hand side so the left hand side is for the reactants and the right hand side is for the products and these sides are determined by the arrow and as you've read this arrow means to form to produce then the plus when it's on the left it simply means reacts with the same plus when it's on the right hand side it simply means and we also have another form of an equation another form of an equation is known as a decomposition where we have one reactant separating into two or more products so where we have one thing it is going to react or to to go through a certain process that is going to enable it to produce two things in this instance we have a that is able to produce B and C so this one can be read as a decomposes into B and C this first one here it can be read as a re act with B to produce C and D let's look at a practical example write down the weight equations of each of the following reactions so what we have in here are chemical sentences so this is just a sentence for example it is saying magnesium metal reacts with oxygen gas to form magnesium oxide now the first thing that you need need to know is once you understand the various forms uh the the features of an equation then it will be easier to write these word equations first of all you know you identify the key features there is this word here which is react with so react with simply Means A Plus on the left side okay uh to form to form simply means an arrow okay to form simply means an arrow so here they said magnesium is reacting with oxygen so this is magnesium plus oxygen is equals to magnesium oxide so the word equation will simply be like this magnesium plus oxygen is equal to magnesium oxide let's look at b b says Ion 2 chloride solution and hydrogen gas are produced okay are produced so we already know what is on the right hand side they've said ion to chloride and hydrogen gas are produced so meaning these are the products and H will be on the right hand side how are they produced when ion react with so again we have seen the react with and the fact that they' said react with means that those particular things are on the left hand side so when ion so ion is on the left hand side reacts with which mean what plus reacts with dilute acid then please take note we are saying Ion 2 chloride solution and hydrogen gas are produced so since they are product this and that is here is going to mean plus so once you are able to F to figure this out then it will be easier for you to write an equation which will be like this ion plus hydrochloric acid is equals to Ion 2 chloride plus hydrogen gas ion reacts with chlorine to form Ion 2 chloride so let's see ion reacts with so reacts with means plus so ion plus chlorine then to form simply means an arrow to form what ion to Chloride so there's only one thing here so as a result we just going to write ion plus chlorine is equal to Ion 2 chloride now let's look at how we can turn these word equations now into equations using symbols write down the word equations below using symbols now in order for you to turn a word equation into an equation using symbols there are two things that you are supposed to know number one you are supposed to know the symbols of particular elements from the periodic table you supposed to know the formulas of radicals you also supposed to know how to construct formulas if you don't know this then you can pause this video and watch the other video in the other in the same playlist about constructing chemical formulas and finding valencies so the first one is we are trying to turn hydrogen and oxygen so hydrogen plus oxygen equals to water we write it into symbols now we know that hydrogen is diatomic so we expect this one is going to be H2 because it's diatomic and when you writing this one in the equation it has to be H2 so all diatomic elements such as hydrogen oxygen nitrogen and all the halogens that is the group seven elements when you are writing them in the equation and only in the equation you are supposed to write them with a subscript of two because they are diatomic you go to hide oxygen also when you check on the periodic table oxygen will just be o but the fact that it's diatomic is telling us that we should write it as O2 then H2O by now any student who has done chemistry or science before should know that the formula of water is H2O hence when when you're writing this equation you're going to come up with this one H2 + O2 is = to H2O and that will be your answer don't worry about the numbers that are in front in the next video we're going to talk about how we balance equations and you understand where these numbers are coming from let's also try to look at this one sodium plus water equal to sodium hydroxide and hydrogen gas so again when you check for sodium on the per iic table sodium is got the symbol n a when you check for Water by now we know water is H2O and then sodium hydroxide we can turn it remember how to come up with formulas you're just going to say sodium is na with a valence of one then hydroxide is O with a valence of one you swap these two you come up with n o you come up with n o so this is the formula then again you meet the high hydrogen hydrogen is diatomic so it's going to be H2 as a result your answer will be like this let's try this one okay so this one was a this one is B this one is C so this is calcium oxide plus hydrochloric acid is equals to that one so again calcium oxide you're going to write your calcium with a valence of two your oxygen with a valence of two after swapping these two the two will come there the two will come there so this is c a and then this is O the two and two cancel as a result the formula will be just be c a and o this this one is our calcium oxide so you found the formula then hydrochloric acid by now everyone should know it it's h c then calcium chloride again it's c a cl2 then water is H2 o now these things we've looked at how to come up with formulas so what we saying is come up with a formula of this one come up with a formula of this one come up with a formula of this one come up with a formula of this one if it's just one element mentioned like the way it was sodium just pick it symbol from the periodic table that's all so if you have forgotten about construction of formulas please revisit the lesson right in this playlist okay so this is how your answer would look like thank you