WEBVTT 00:00:03.300 --> 00:00:06.810 - WELCOME TO PART ONE OF THE VIDEO TUTORIAL SERIES 00:00:07.060 --> 00:00:08.840 ON CHEMICAL REACTIONS. 00:00:09.090 --> 00:00:11.630 IN THIS FIRST TUTORIAL, 00:00:11.780 --> 00:00:14.480 WE WILL LOOK AT BALANCE IN CHEMICAL REACTIONS. 00:00:14.630 --> 00:00:16.690 LET'S GET STARTED. 00:00:16.840 --> 00:00:22.000 SO CHEMICAL REACTIONS OBEY THE LAW OF CONSERVATION OF MASS, 00:00:22.150 --> 00:00:39.390 THAT MEANS THAT ATOMS ARE NEITHER CREATED NOR DESTROYED. 00:00:39.540 --> 00:00:40.450 ALL RIGHT. 00:00:40.600 --> 00:00:42.360 SO WHAT'S HAPPENING RIGHT, 00:00:42.510 --> 00:00:56.750 IS THAT THE CHEMICAL BONDS ARE BEING BROKEN AND FORMED. 00:00:57.000 --> 00:00:59.570 OKAY. SO REALLY A CHEMICAL REACTION IS SIMPLY 00:00:59.720 --> 00:01:03.180 ABOUT REARRANGING HOW THE ATOMS ARE CONNECTED 00:01:03.330 --> 00:01:05.810 THROUGH THE BONDS, ALL RIGHT. 00:01:06.060 --> 00:01:08.810 SO LET'S LOOK AT AN EXAMPLE. 00:01:09.060 --> 00:01:14.840 SO HERE, WE HAVE METHANE REACTING WITH OXYGEN 00:01:15.090 --> 00:01:20.570 TO PRODUCE CARBON DIOXIDE AND WATER. 00:01:20.720 --> 00:01:24.270 IF WE LOOK AT THIS FROM A VERY PHYSICAL PERSPECTIVE, 00:01:24.420 --> 00:01:29.510 WE COULD LOOK AT THE MOLAR MASS OF METHANE SO-- 00:01:29.660 --> 00:01:32.120 AND SINCE THERE'S ONE MOLE REACTING 00:01:32.270 --> 00:01:36.420 WE WOULD PUT 16.05 GRAMS, 00:01:36.570 --> 00:01:39.630 WE WOULD HAVE TWO MOLES OF OXYGEN, 00:01:39.780 --> 00:01:45.210 SO THAT WOULD CORRESPOND TO 64 GRAMS OF OXYGEN 00:01:45.360 --> 00:01:48.180 AND THEN WE CAN LOOK AT OUR ARROW LIKE WE WOULD, 00:01:48.330 --> 00:01:51.450 AN EQUAL SIGN OF MATHEMATICS AND IF WE LOOK AT, 00:01:51.600 --> 00:01:58.660 THERE'D BE ONE MOLE OF CARBON DIOXIDE 44.01 GRAMS, 00:01:58.810 --> 00:02:03.420 AND THEN LAST BUT NOT LEAST TWO MOLES OF WATER, 00:02:03.570 --> 00:02:08.840 33.04 GRAMS, AND THEN WE DO PRODUCE HEAT AND WE'LL 00:02:09.090 --> 00:02:14.630 TALK ABOUT IN A LATER TUTORIAL LOOKING AT THE ENERGY CHANGES 00:02:14.780 --> 00:02:17.210 THAT OCCUR WITH CHEMICAL REACTIONS. 00:02:17.360 --> 00:02:19.870 SO IF WE LOOK HERE WE SEE THAT ALL TOGETHER, 00:02:20.120 --> 00:02:26.600 WE STARTED WITH 80.05 GRAMS OF MATERIAL 00:02:26.750 --> 00:02:29.150 AND WHEN WE'RE ALL DONE, 00:02:29.300 --> 00:02:32.300 WE HAVE 80.05 GRAMS. 00:02:32.450 --> 00:02:35.870 SO WE SAY THE MASS IS CONSERVED. 00:02:36.120 --> 00:02:40.060 WE CAN ALSO LOOK AT IT FROM THE POINT OF THE ATOMS, 00:02:40.210 --> 00:02:43.660 ON THE LEFT WE SEE WE HAVE ONE CARBON, 00:02:43.810 --> 00:02:48.060 FOUR HYDROGENS AND FOUR OXYGENS. 00:02:48.210 --> 00:02:53.330 AND ON THE RIGHT WE HAVE ONE CARBON, 00:02:53.480 --> 00:02:56.720 FOUR HYDROGENS AND FOUR OXYGENS. 00:02:56.870 --> 00:03:02.360 SO WE HAVE ALSO MAINTAINED THE SAME NUMBER OF ATOMS 00:03:02.510 --> 00:03:04.120 SO THAT'S WHAT WE TALK ABOUT THAT ATOMS 00:03:04.270 --> 00:03:06.720 ARE NOT CREATED NOR DESTROYED. 00:03:06.870 --> 00:03:08.210 ALL RIGHTY. 00:03:08.360 --> 00:03:11.720 NOW, LET'S GO INTO THE ACTUAL TECHNIQUE 00:03:11.870 --> 00:03:15.000 OF BALANCING CHEMICAL REACTIONS. 00:03:15.150 --> 00:03:18.210 SO LINGUISTICALLY THE COEFFICIENT IS THE NUMBER 00:03:18.360 --> 00:03:21.240 PLACED IN FRONT OF THE CHEMICAL REACTION, 00:03:21.390 --> 00:03:25.810 RIGHT, SO THE COEFFICIENTS ARE HERE, NOTICE, 00:03:26.060 --> 00:03:27.870 THAT WE NEVER SHOW THE ONES, 00:03:28.120 --> 00:03:36.720 THE ONES ARE UNDERSTOOD. 00:03:36.870 --> 00:03:38.030 ALL RIGHT. 00:03:38.180 --> 00:03:41.720 NOW WE HAVE THE OPTION TO PUT IN SUBSCRIPTS 00:03:41.870 --> 00:03:44.090 TO INDICATE THE PHYSICAL STATE 00:03:44.240 --> 00:03:47.480 OF THE REACTANTS IN PRODUCTS AND YOU'VE SEEN THESE BEFORE, 00:03:47.630 --> 00:03:53.450 RIGHT, S FOR SOLID, G FOR GAS, L FOR LIQUID AND AQ 00:03:53.600 --> 00:03:56.630 WHEN WE'VE DISSOLVED THE SUBSTANCE IN WATER. 00:03:56.780 --> 00:03:58.450 SO THE RULES FOR OUR CORRECT 00:03:58.600 --> 00:04:01.210 CHEMICAL EQUATION ARE VERY STRAIGHTFORWARD. 00:04:01.360 --> 00:04:04.690 IT HAS TO BE CONSISTENT WITH THE EXPERIMENTAL FACTS, 00:04:04.840 --> 00:04:07.180 WE'RE ONLY GOING TO LIST REACTANTS AND PRODUCTS 00:04:07.330 --> 00:04:09.810 IF THEY'RE ACTUALLY INVOLVED IN THE REACTION 00:04:10.060 --> 00:04:13.450 AND WE ALWAYS HAVE TO USE THE CHEMICAL FORMULA, 00:04:13.600 --> 00:04:15.090 CORRECT CHEMICAL FORMULA. 00:04:15.240 --> 00:04:17.270 NOW, REMEMBER THAT THE CHEMICAL FORMULAS 00:04:17.420 --> 00:04:22.330 COME FROM THE VALENCE ELECTRONS AND THE OCTET RULE. 00:04:22.480 --> 00:04:25.150 SO WE DON'T HAVE THE FREEDOM TO CHANGE THAT, 00:04:25.300 --> 00:04:27.360 THAT'S OUT OF OUR CONTROL. 00:04:27.510 --> 00:04:31.570 AND SO TO BALANCE, IT'S FOCUSING ON THE COEFFICIENT'S, 00:04:31.720 --> 00:04:34.630 THE COEFFICIENT'S GIVE US THE RATIOS 00:04:34.780 --> 00:04:38.780 AND WE MUST OBEY THE CONSERVATION OF MASS. 00:04:39.030 --> 00:04:41.090 SO NOW THAT WE HAVE AN OVERVIEW, 00:04:41.240 --> 00:04:50.480 LET'S PRACTICE BALANCING SOME REACTIONS. OKAY. 00:04:50.630 --> 00:04:54.780 SO BASICALLY THE FIRST THING WE WANT TO DO IS THIS-- 00:04:55.030 --> 00:04:57.480 IS LOOK BACK AND ASSESS THE EQUATION, 00:04:57.630 --> 00:04:59.390 LOOKING AT THE NUMBER OF ATOMS 00:04:59.540 --> 00:05:02.630 OF EACH ELEMENT ON THE REACTANT IN THE PRODUCT SIDE, 00:05:02.780 --> 00:05:07.510 RIGHT IF THE TWO NUMBERS DO NOT MATCH THEN IT'S NOT BALANCE, 00:05:07.660 --> 00:05:10.120 SO WE GOT TO GET TO WORK, ALL RIGHT. 00:05:10.270 --> 00:05:14.000 SO WE'RE GOING TO BALANCE ONE ELEMENT AT A TIME, 00:05:14.150 --> 00:05:17.720 ALL RIGHT, BY ADDING COEFFICIENTS, RIGHT. 00:05:17.870 --> 00:05:21.660 WE NEVER CHANGE THE CHEMICAL FORMULA, RIGHT, 00:05:21.810 --> 00:05:27.840 THAT COMES FROM VALENCE ELECTRONS AND THE OCTET RULE. 00:05:28.090 --> 00:05:30.060 SO WE'RE ALL WISE AND POWERFUL 00:05:30.210 --> 00:05:33.720 BUT WE DON'T GET TO MESS WITH THE OCTET RULE. 00:05:33.870 --> 00:05:36.060 A COEFFICIENT APPLIES TO-- 00:05:36.210 --> 00:05:38.750 RIGHT TO EVERY ELEMENT IN THE FORMULA, 00:05:39.000 --> 00:05:41.570 SO IT'S A BLENDING OF ENGLISH AND MATH, 00:05:41.720 --> 00:05:45.510 IT'S A GOOD IDEA TO SAVE SINGLE ELEMENTS-- 00:05:45.660 --> 00:05:48.780 SINGLE ELEMENT PRODUCTS AND REACTANTS FOR LAST 00:05:49.030 --> 00:05:51.450 BECAUSE YOU'RE ONLY INFLUENCING ONE ELEMENT-- 00:05:51.600 --> 00:05:54.120 ONE ELEMENT AT A TIME. 00:05:54.270 --> 00:05:56.750 AND THEN REMEMBER THAT THE COEFFICIENT'S ALWAYS 00:05:57.000 --> 00:06:00.480 NEED TO BE THE SMALLEST SET OF WHOLE NUMBERS. 00:06:00.630 --> 00:06:04.000 WHEN YOU'RE ALL DONE, STEP BACK AND LOOK, 00:06:04.150 --> 00:06:05.750 MAKE SURE YOUR COEFFICIENTS 00:06:06.000 --> 00:06:09.540 CANNOT BE DIVIDED BY A COMMON FACTOR. 00:06:09.690 --> 00:06:12.030 ALL RIGHTY. 00:06:12.180 --> 00:06:16.090 NOW LET'S PRACTICE TOGETHER. ALL RIGHT. 00:06:16.240 --> 00:06:19.180 SO HERE WE HAVE ALUMINUM REACTING 00:06:19.330 --> 00:06:23.090 WITH OXYGEN TO PRODUCE ALUMINUM OXIDE, 00:06:23.240 --> 00:06:28.240 SO SINCE OXYGEN AND ALUMINUM ARE BOTH BY THEMSELVES, 00:06:28.390 --> 00:06:34.240 WE'LL FOCUS ON WHERE THEY'RE MIX TOGETHER AND WE COULD GO-- OOH, 00:06:34.390 --> 00:06:37.090 THERE'S TWO OF THOSE, WE'LL PUT A TWO THERE. 00:06:37.240 --> 00:06:38.450 AND LET'S-- 00:06:38.600 --> 00:06:41.060 SO LET'S JUST DO THAT, ALL RIGHT SO WE PUT A TWO 00:06:41.210 --> 00:06:43.510 IN FRONT OF THE ALUMINUM AND THEN WE'RE LIKE, 00:06:43.660 --> 00:06:47.780 HMM, OXYGEN, THERE'S THREE BUT IT'S DIATOMIC. 00:06:48.030 --> 00:06:51.870 SO WE'LL HAVE TO PUT A THREE OVER TWO, RIGHT, 00:06:52.120 --> 00:06:54.870 BECAUSE 3/2 X 2/1, THE TWOS 00:06:55.120 --> 00:07:02.360 WILL CANCEL AND WILL END UP WITH THE THREE OXYGENS. 00:07:02.510 --> 00:07:05.750 BUT NOW THIS IS GOING TO VIOLATE OUR RULE 00:07:06.000 --> 00:07:08.090 THAT WE HAVE TO HAVE WHOLE NUMBERS. 00:07:08.240 --> 00:07:12.570 SO WE'LL TREAT THIS [INAUDIBLE] ALGEBRAIC EXPRESSION 00:07:12.720 --> 00:07:19.390 AND WE'LL MULTIPLE THE ENTIRE EQUATION BY THE FACTOR OF TWO. 00:07:19.540 --> 00:07:22.810 SO THAT WILL GIVE US OUR BALANCED REACTION 00:07:23.060 --> 00:07:28.870 FOR ALUMINUM ATOMS OR FOUR MOLES WILL REACT WITH THREE MOLES 00:07:29.120 --> 00:07:38.300 OF OXYGEN TO PRODUCE TWO MOLES OF ALUMINUM OXIDE. 00:07:38.450 --> 00:07:40.390 ALL RIGHT. 00:07:40.540 --> 00:07:44.360 NOW LET'S TRY ANOTHER ONE. ALL RIGHTY. 00:07:44.510 --> 00:07:46.810 SO HERE, EVERYTHING ALL OF-- 00:07:47.060 --> 00:07:49.840 THEY'RE ALL COMPOUNDS WITH MIXED ELEMENTS 00:07:50.090 --> 00:07:52.600 SO WE JUST PICK A PLACE TO START, 00:07:52.750 --> 00:07:57.000 MY EXPERIENCE I PICK AN ATOM AND I DO BEST, 00:07:57.150 --> 00:08:01.300 IF I FIND MYSELF GETTING STUCK, I START OVER FRESH 00:08:01.450 --> 00:08:04.210 AND BEGIN WITH A DIFFERENT ELEMENT THAT SEEMS TO BE 00:08:04.360 --> 00:08:08.090 ALL IT TAKES TO GET UNSTUCK IN THIS TYPE OF QUESTION. 00:08:08.240 --> 00:08:09.570 ALL RIGHTY. 00:08:09.720 --> 00:08:13.510 WELL, THE PHOSPHORUSES ARE BOTH ONES, SO WE'LL WAIT THERE. 00:08:13.660 --> 00:08:17.390 WE SEE FIVE CHLORINES AND ONE CHLORINE, 00:08:17.540 --> 00:08:22.600 SO THAT WOULD LET US KNOW WE SHOULD PUT A FIVE HERE 00:08:22.750 --> 00:08:25.720 AND THEN THE OXYGENS, WE HAVE ONE OXYGEN 00:08:25.870 --> 00:08:30.150 AND WE HAVE FOUR OXYGENS SO WE'LL PUT A FOUR HERE. 00:08:30.300 --> 00:08:31.870 NOW THE MOMENT OF TRUTH, 00:08:32.120 --> 00:08:35.720 LET'S LOOK AT THOSE HYDROGENS AND SEE WHAT'S GOING ON. 00:08:35.870 --> 00:08:40.750 ON THE LEFT 4X2 WE HAVE EIGHT HYDROGENS 00:08:41.000 --> 00:08:45.270 AND THEN WE HAVE THREE HYDROGENS FROM THE PHOSPHORIC ACID 00:08:45.420 --> 00:08:52.180 AND FIVE HYDROGENS FROM THE HYDROCHLORIC AND SO VOILA. 00:08:52.330 --> 00:08:59.210 OUR REACTION IS BALANCED. OKAY. 00:08:59.360 --> 00:09:03.840 LET'S TRY ANOTHER ONE HERE 00:09:04.090 --> 00:09:07.600 THE BARIUMS ONE TO ONE LOOKS GREAT, 00:09:07.750 --> 00:09:12.420 WE HAVE TWO OXYGENS BUT WE HAVE THREE OVER HERE, 00:09:12.570 --> 00:09:15.000 WELL WOULDN'T IT BE SIMPLER IF THERE WAS JUST ONE, 00:09:15.150 --> 00:09:17.750 SO I'D SAY WE CAN MULTIPLY THAT BY ONE HALF, 00:09:18.000 --> 00:09:21.540 RIGHT 1/2 X 2 WOULD BE ONE BUT OF COURSE, 00:09:21.690 --> 00:09:24.600 NOW WE'VE INTRODUCED A FRACTIONAL COEFFICIENT, 00:09:24.750 --> 00:09:27.720 SO WE'LL USE THAT SAME STRATEGY 00:09:27.870 --> 00:09:33.360 AND MULTIPLY THE ENTIRE EXPRESSION BY TWO 00:09:33.510 --> 00:09:41.180 TO GET OUR BALANCED EQUATION SO TWO MOLES 00:09:41.330 --> 00:09:50.030 OF BARIUM PEROXIDE PRODUCED TWO MOLES OF BARIUM OXIDE 00:09:50.180 --> 00:09:54.690 AND A MOLE OF OXYGEN, OKAY. 00:09:54.840 --> 00:09:59.480 AND THEN THERE IS A SEPARATE VIDEO TUTORIAL ON THIS REACTION, 00:09:59.630 --> 00:10:01.390 THIS IS A COMBUSTION REACTION 00:10:01.540 --> 00:10:04.630 BUT I THINK IT'S WORTH TAKING THE TIME TO DO ONE 00:10:04.780 --> 00:10:07.390 HERE AS WELL. 00:10:07.540 --> 00:10:09.210 SO REMEMBERING WITH COMBUSTION REACTIONS 00:10:09.360 --> 00:10:11.540 WE WANT TO START WITH THE CARBONS 00:10:11.690 --> 00:10:15.570 SO WE HAVE FIVE ON THE LEFT SO WE WOULD NEED FIVE 00:10:15.720 --> 00:10:20.150 CO2S AND THEN WE HAVE TEN HYDROGENS, 00:10:20.300 --> 00:10:24.000 SO WE WOULD NEED FIVE WATERS SO 00:10:24.150 --> 00:10:27.300 WE LOOK AT ALL OF THE OXYGENS ON THE RIGHT, 00:10:27.450 --> 00:10:34.630 WE HAVE A FIVE AND THEN THERE'S TWO IN EACH CO2 00:10:34.780 --> 00:10:38.240 AND THEN WE HAVE A FIVE COEFFICIENT IN FRONT OF WATER, 00:10:38.390 --> 00:10:40.060 EACH WATER HAS ONE, 00:10:40.210 --> 00:10:43.540 SO THAT LEAVES US WITH FIFTEEN OXYGENS, 00:10:43.690 --> 00:10:50.180 OXYGEN IS HIGH MAINTENANCE, RIGHT SO WE'RE BACK TO 15/2 00:10:50.330 --> 00:10:55.360 AND ONCE AGAIN WE WILL MULTIPLY THE ENTIRE EXPRESSION 00:10:55.510 --> 00:11:00.840 BY TWO TO CLEAR THOSE FRACTIONAL COEFFICIENTS 00:11:01.090 --> 00:11:06.090 AND I'LL SIDE THIS UP JUST A WEE BIT MORE 00:11:06.240 --> 00:11:10.240 AND WE'LL PUT OUR FINAL ANSWER TO-- 00:11:10.390 --> 00:11:21.150 OF THE HYDRO CARBONS REACTS WITH 15 OXYGEN TO PRODUCE 10 CO2 00:11:21.300 --> 00:11:26.330 AND 10-- OOPS 10 WATERS. 00:11:26.480 --> 00:11:31.360 OKAY. SO THAT CONCLUDES OUR VIDEO TUTORIAL 00:11:31.510 --> 00:11:33.720 ON BALANCING CHEMICAL REACTIONS, 00:11:33.870 --> 00:11:36.690 THIS WOULD BE A GREAT TIME TO WORK A FEW MORE PROBLEMS 00:11:36.840 --> 00:11:39.480 TO REINFORCE YOUR UNDERSTANDING.