hi everyone this is going to be our practice test answer key uh the video of me taking this and giving helpful hints and strategies for our upcoming tests that we have and uh i'm going to go ahead and start with target one which states i can identify the components of a chemical reaction well this is a chemical reaction here and let's put the different parts let's put them in there and label what they are it says use the information in the ovals below to fill in the boxes to write a chemical equation so a chemical equation uh starts with reactants and ends with products and there is a yield sign in the middle so in this case we have it right here this large box is going to yield there's my arrow so that one's going to go there these two smaller boxes and there's going to be the plus signs going to be in between those two so i already have the plus sign in here these are our reactants so it's 6 h2o plus 6 co2 so 6 water molecules plus 6 carbon dioxide molecules yields c6h12o6 which is glucose plus six oxygen molecules and that's actually photosynthesis right there so there's the answers these all here this is where they would belong here and it says draw an arrow from each word above to label the parts of a chemical reaction so i'll start out with coefficients a coefficient is one of those large numbers that we use to balance a chemical reaction the reactants are what we start out with so the reactants are is all these things right here the water and the carbon dioxide a subscript is one of these small little numbers here so there's the subscript that's there's a subscript there and there and there and there and there those are subscripts products are what you make in a chemical reaction so these the glucose and oxygen are products and the yield sign that's the arrow sort of i imagine it like an equal sign so that is target one i can identify the components of a chemical now reaction to target two i can explain what happens to atoms when a chemical reaction occurs and determine if it is exothermic or endothermic well there's two vocab words right there and let's go ahead and start this first section questions one through four chemical reactions that release energy well when they release energy that means energy is given off and remember how i told you i remember it bugs have an exoskeleton insects do and that means they're skeletons on the outside so i always remember the prefix exo meaning outside so if they give off energy to the outside that is a exothermic reaction now the opposite is endo meaning inside because you and i we have endoskeletons so if chemical reactions absorb energy energy goes into them to the inside that is endothermic so that is endothermic reactions now what about energy needed to get a chemical reaction started that is something called activation energy that we talked about and the word activation means to start so that's the term from our reading and from demonstrations in class that you need to activate some chemical reactions you have to use activation energy how about number four in your own words explain what happens to atoms when a chemical reaction occurs so let me draw that for you real quick here so we got these different molecules or atoms and you know it really could be anything and then we could make it just generic molecules well what happens in my own words it is the bonds between these atoms are all broken and rearranged in new different i guess you'd call them new different uh organizations they make new bonds so these bonds break apart and new bonds are formed so if i had one two three four five six over on this side i'd have to have one two three four five six on this side as well okay these could be different molecules right here but if i have one two three four five six i have to have one two three four five six who knows those are just generic molecules there but in my own words i guess i would say what happens is um bonds between atoms are broken and new new bonds form and they create new and different molecules on this side still the same atoms they're just rearranged i like the term rearranging questions five through eight categorize the following examples as exothermic or endothermic again remember exo means heat's given off to the outside during the reaction in endothermic heat is or energy i should say it doesn't have to be heat is taken in but food digesting in your stomach the whole purpose of digesting food is to break apart those bonds and release the energy for you to use in your daily life so that is an exothermic reaction burning leaves to start a campfire while there's lots of energy given off there in the form of light and heat that again is an exothermic reaction how about baking a loaf of bread well you mix those ingredients together you put them in the oven and the heat goes in inside right that's the whole point of cooking something generally baking a loaf of bread is an endothermic reaction plants using sunlight in the process of photosynthesis right they take water and carbon dioxide and take in sunlight to help it out and it makes glucose and oxygen so that sunlight being absorbed right taken in is another example of endo thermic reaction so 5 and 6 are exo 7 and 8 are endo in this quiz on to target 3. so target 3 for unit 4 says i can balance a chemical equation based on the law of conservation of matter all right well here it says balance the four chemical equations below if just if just the molecules are shown write the chemical equation first and then balance it well they're not for the first two so let's go ahead and do these so if i go ahead and do it this way i have phosphorus and oxygen in this side and again i must have phosphorus and oxygen on this side i have one and two oxygens over here over here i got two and five oxygens so i'll go ahead and start with my oxygens i have two over here and five over here that means i'm going to have to make both of these equal to 10 in order to get because you can't get two into five you can't have a half of an atom that would cause some very bad things to happen so i'm going to make both of these the lowest common denominator is 10. so over here i'm gonna have to multiply this one by five so five times o2 means i'm going to have 10 total oxygens and over here i'm going to have to multiply this by 2. so the 2 goes to my phosphorus which means i double that to 4 and my 2 goes to my oxygen which doubles it to 10 okay that's that's fine now my oxygens are good my phosphorus is i have 4 over here 1 over here i just have to multiply that by 4 and now i get 4 there and everything's balanced up and that is a balanced chemical equation okay time for this one here we got a little bit more in-depth one here this one's a little harder because there's more to it i see one two three four five different atoms in here looks like we have aluminum we have chlorine we have hydrogen we have sulfur and we have oxygen five atoms alclh write them over here al cl h s and o now i gotta do my counting here aluminum one chlorine three hydrogen two sulfur just one and oxygen four and this side aluminum two sulfurs yeah through one but remember everything in the parenthesis is multiplied by three here so sulfurs i actually have three oxygen four times three is twelve well a lot of those chlorine one and hydrogen one so there's my tallies so far i can see they're not balanced look at that 12. the first thing i'm going to do is go ahead and balance my oxygens so i have 4 over here and i have 12 over here so 4 does go into 12 i just need to multiply this by 3. so that 3 transfers to everything in here this is actually sulfuric acid h2so4 so i'm going to need three molecules of that so my 3 times my two h's makes my h is six now my three times my one sulfur three and my three times my four oxygens is twelve okay oh my sulfurs just took care of themselves how nice right here i have six hydrogens and only one over here wow i'm gonna have to multiply this by six so my six goes to my hydrogen makes that six my chlorines are now six and if i go over here i have chlorine six and over here three my aluminums are one and that's two so if i double this aluminum put the two there my two goes to my al makes it two my two goes to my cl makes this six and that is balanced up very nice so there it is a little bit harder i'll probably give you one like that on your test one like this one medium one and one like this now on to these two sometimes there's some confusion here the only difference is you have to write out the equation first before you balance it so right here i'm going to write it underneath we're starting out with an atom of sodium now spread it out here and we have two chlorines so this is a cl2 molecule here's my arrow okay and right here i got an n a and a cl one of each and one molecule so that is table salt nacl i like to put these lines in front of it and i teach my students to do that so they know where they can put the coefficients at this point there's no more messing around with subscripts that's only to count how many atoms you have in each molecule so if i go ahead and use the point method for this one i have one sodium here and one sodium here okay one there one there so i'm okay with those chlorines i have two on this side and one on this side so i'm gonna have to double this to two that two goes to my chlorine so two chlorines two chlorines good there how about my sodiums i have two nas here now and i only had one so if i put my two there looks like i have two sodiums two sodiums two chlorines two chlorines that was a pretty easy one finished equation how about this one right here looks like i have a nitrogen gas molecule an n2 plus an h2 in when those two combine or react i should say they make a nh3 so an n h3 just like that okay let's balance it up here i have n's and h's on this side i have n's in h's on this side two n's two h's one n and three h's let's go ahead and take care of the h's first i have two and then three and they're both in one spot so i have to make two and three both equal to six in this case so that's a two so two times my n is 2 and my 2 times 3 for h is a 6. now i have 6 h i'm going to have to multiply this one by 3. 3 times 2 is 6. and lo and behold my ends were already taken care of now there is my final balanced equation went from this to this in your own words explain the law of conservation matter well here's what it means to me let me go ahead and draw this one out for you because there's an n2 and we have h2 here and those things rearrange to form this that's what happens but here's the problem i have two ends and four h's cannot make something with one n and three h's and where'd the other where'd this end go where'd this other age come from that's the whole purpose we have to balance and that's what the law of conservation of matter means it means we're gonna have to have 1 and 2 plus 3 of these h2s it's probably not a very good drawing there's another one here h get rid of that one and here's our other one it's small don't have a lot of room but i need in total six h's one two three four five six and i'm gonna have to have in the end it's gonna make if i combine n2 and three h2s what i'm gonna make in the process are two of these nh3 molecules like that because i have six h's one two three four five six h's one two ends one two ends and that's the whole thing of what we're really talking about so if i explain that in my own words is the mass of the reactants which is this side of the arrow has to equal the mass of the products has to be an equal number of each type of element on both sides of the arrow that's how i would explain that and our last target here target four i can explain the four ways to change the rate of a chemical reaction now we've spent a lot of time this last week and a half going over this doing demonstrations running a lab ourself with alka-seltzer tablets in school now it'd be impossible to understand these if you didn't know what the four are so i'm going to go ahead and write those four right here and the first thing you can do is and i'm going to draw a triangle here which in math means change it's delta symbol you can change the temperature you can heat something up or cool it down and the reaction is going to either increase or decrease based on what you do you can change the temperature you can also change the surface area you can change the surface area of the reactants you can chop them up make them go faster or slow them down by doing the opposite another thing you can do is change the concentration and what that means is you're changing the concentrate how concentrated the reactants are maybe you're using only half concentrated 50 concentrated an acid some sort of acid to react a metal what if you change that to 100 concentration full concentration i bet you would speed things up or if you wanted to slow it down you can dilute it with water and the last thing you can do i don't need my delta symbol there is you can add a catalyst a catalyst is something that speeds up a chemical reaction and it's also not used up in the process so many times in industry and when we're in the manufacturing process when catalysts are used you get them back and use those catalysts over and over and over again to speed up chemical reactions and by the way you have your own catalysts in your body if a living thing makes its own catalyst it's called an enzyme and one of the enzymes in our body is pepsin and it's something that is used in your digestive system it's added in to help you digest meat faster that's an enzyme which is a biological catalyst so now that we know our four ways here we can change the temperature the surface area or the concentration of the reactants we can also add a catalyst let's go ahead and answer these four questions here a science teacher wants to teach her students about changing the rate of a chemical reaction she shows her students four different experiments using the same materials the results of each experiment are listed below for each result given tell which of the four ways to change the rate of a chemical reaction was demonstrated the first one a 25 gram piece of zinc took 55 seconds to completely react with hydrochloric acid the same amount of zinc in powdered form took only 28 seconds to completely react with hydrochloric acid well she was demonstrating that if you change the surface area by chopping something up the surface area she was chopping it up grinding it up powdering it she really really at that point would really really be increasing the surface area if you don't remember that you could go back to the notes that i sent out on top about target four with changing the surface area of something but that's clearly what she's doing right there number six says a 25 gram piece of zinc took 55 seconds to completely react with hydrochloric acid at 24 degrees celsius now another 25 piece gram piece of zinc took 28 seconds to completely react with hydrochloric acid at 44 degrees celsius so that was a lot warmer so what she was doing there was changing the temperature she changed the temperature and increased the speed at which that reaction takes place which makes sense because the atoms in order to react have to bump into each other and when you warm things up you're increasing their energy so there's more movement which has a greater chance for things to bump into each other faster changing the temperature number seven a 25 gram piece of zinc took 55 seconds to completely react with a mixture of 50 hydrochloric acid and 50 water another 25 gram piece of zinc took only 28 seconds to completely react with a mixture of 80 hydrochloric acid and 20 percent water so this second one was a lot more concentrated she was changing the concentration this is a lot probably a lot more powerful hydrochloric acid because it's almost pure with 20 percent and this one is half water half hydrochloric acid that makes sense that this one would uh would react faster and the last one two experiments were set up both containing 25 gram pieces of zinc in the first one the zinc completely reacted with hydrochloric acid in 55 seconds in the second experiment a small amount of copper sulfate copper sulfate was added to the zinc and hydrochloric acid and this reaction only took 28 seconds well that's a clear example of making a reaction go faster i always do that making a reaction go faster by adding a catalyst so copper sulfate is a catalyst in the reaction of zinc and hydrochloric acid so that's our practice test that's the answers and i would say this is uh dok level probably two right here this is definitely a dok level of one this here would be a dok level of probably one up here i would say this is more of a two question these here are probably twos and this here is the level three d okay so that's going to be on the second portion of your test the level three four portion and you're also going to have a lab that resembles the lab we did in class where you are asked to run an experiment and you're going to have to understand the variables and what's happening and write answers that would fit likely fit and graph your information so make sure you understand how to label remind yourself how a correct title for a graph goes the effect of the blank on the blank and make sure you are thinking about what types of graphs are used for certain situations do i need a bar graph here do i need a line graph here what one makes more sense and that's going to be the level four portion uh of your ex of your unit four test so that is the video of the practice test with helpful hints you're going to have a bit more multiple choice i like to make the target quiz a little bit harder some of the stuff you're going to have is bubble in but you'll be doing this part yourself along with the level 4 when you run your experiment so that's all i can say about that that i can think of hopefully you're doing a good job studying here and ready for this target ready for this unit 4 chemical reactions test