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4 Salt in water:
4 Burning sulphur:
3 STOP THE TAPE!
3 START THE TAPE
3 PHYSICAL and CHEMICAL CHANGES
3 ;"Software"
3 ;"Press:";
3 ;"Press any key to continue":
3 ;"MA (Cantab.), MA (London)"
3 ;"Educational"
3 ;"CP Lawrence";
3 "press ENTER to continue ";
3 "g"+n,usr:
3 "f"+n,usr:
3 to repeat this program";
3 to load the next program";
3
2 w$="11040002":
2 w$="04040400":
2 reversible
2 redistribution
2 kinetic theory
2 energy change
2 e$="etc.":
2 The RATE of a CHEMICAL REACTION
2 ENERGY CHANGES
2 CHEMICAL CHANGE
2 ;"their surroundings"
2 ;"finished burning, the";
2 ''"In a physical change there is"'"
2 ''"Examples of
2 '"What is a
2 '"In a chemical change there is"'"
2 "t"+n,usr:
2 "r"+n,usr:
2 "o"+n,usr:
2 "l"+n,usr:
2 "k"+n,usr:
2 "j"+n,usr:
2 "h"+n,usr:
2 "d"+n,usr:
2 "b"+n,usr:
2 "a"+n,usr:
2 of the reaction."
2 how the concentration of a";
2 changes:"
2 change?":
2 change occurs."
1 w$="19000231":
1 w$="18000331":
1 w$="18000329":
1 w$="17050022":
1 w$="17000331":
1 w$="15070400":
1 w$="15010530":
1 w$="15000531":
1 w$="15000429":
1 w$="14000330":
1 w$="13270300":
1 w$="13060320":
1 w$="13050300":
1 w$="13000731":
1 w$="12050300":
1 w$="12050022":
1 w$="11050121":
1 w$="11000431":
1 w$="09140008":
1 w$="09050022":
1 w$="09050017":
1 w$="09050007":
1 w$="08020224":
1 w$="08020004":
1 w$="07100219":
1 w$="07000631":
1 w$="06130008":
1 w$="06050016":
1 w$="06050006":
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1 w$="05270300":
1 w$="05090321":
1 w$="05060320":
1 w$="05050300":
1 w$="05040627":
1 w$="04050022":
1 w$="04020224":
1 w$="03090922":
1 w$="03060800":
1 w$="03010606":
1 w$="030043078150575":
1 w$="02281303":
1 w$="02101317":
1 w$="02001309":
1 w$="02000831":
1 w$="02000330":
1 w$="00171914":
1 w$="00021914":
1 usually a change or redistribu-
1 total time
1 total mass of carbon dioxide
1 tion of mass
1 surface area
1 substances
1 redistribution of
1 particles colliding
1 often a great energy change
1 not easily reversible
1 not easily
1 no new substances are formed
1 no great energy change
1 no change or redistribution of
1 no change or
1 new substance
1 latent heat)
1 latent heat
1 latent energy
1 large energy
1 easily reversible
1 e$="reduction":
1 e$="oxidation":
1 e$="melting":
1 e$="evaporation":
1 e$="double decomposition":
1 e$="dissolution":
1 e$="displacement":
1 e$="decomposition":
1 e$="crystallisation":
1 e$="combination":
1 e$="boiling":
1 changes often
1 averagespeed
1 average speed
1 at least one new substance is
1 at least one
1 are formed
1 a3
1 a2 aP
1 a1 4=
1 TEMPERATURE
1 SURFACE AREA
1 RATE of REACTION
1 Kinetic energy
1 H is"'" negative."
1 H is positive."
1 H = -286 kJ"
1 H = +90.3 kJ"
1 FACTORS AFFECTING REACTION RATE
1 DISSOLVING SALT in WATER
1 Created with Ramsoft MakeTZX
1 CONCENTRATION
1 CHEMICAL ENERGY
1 Bond energy
1 BURNING SULPHUR in AIR
1 ;"would mean '2 moles of";
1 ;"would have been
1 ;"would be discovered";
1 ;"with a blue flame.":
1 ;"ually disappear.":
1 ;"tration of hydrochloric acid";
1 ;"to do work."
1 ;"to an amber coloured";
1 ;"time. Only the rate changes."
1 ;"time it takes for the";
1 ;"ticles are already tightly";
1 ;"thiosulphate solution";
1 ;"therefore more likelihood of";
1 ;"there is no great";
1 ;"the start of each experiment."
1 ;"the same point."
1 ;"the same depth each time, so";
1 ;"the reaction, then gradually";
1 ;"the gas jar."
1 ;"the cross should disappear";
1 ;"the air is used up when";
1 ;"that the rate has been";
1 ;"tents at time t,"
1 ;"sulphur has been formed."
1 ;"sulphur burns."
1 ;"substances";
1 ;"stopclock."
1 ;"steam had been produced,
1 ;"stances."
1 ;"spoon will be left";
1 ;"solution into the jar.":
1 ;"solid disappeared..."
1 ;"slows down."
1 ;"salt in a beaker.":
1 ;"roll sulphur on a";
1 ;"release heat to";
1 ;"reaction going."
1 ;"reactant decreases with";
1 ;"pungent smelling gas in";
1 ;"product increases with time"
1 ;"produced is the same each";
1 ;"presents to the liquid."
1 ;"packed."
1 ;"oxygen were known, it";
1 ;"or into electricity first, and then into heat and light."
1 ;"or * both."
1 ;"or * a chemical change;":
1 ;"once it is alight the";
1 ;"nothing."
1 ;"ning..."
1 ;"minutes":
1 ;"mass of oxygen + mass of sulphur"
1 ;"marble chips,"
1 ;"liquid.":
1 ;"is decreasing all the time";
1 ;"initial rate of reaction."
1 ;"hydrochloric acid."
1 ;"hydrochloric acid'.)"
1 ;"hydrochloric acid (2";
1 ;"horizontal straight line at";
1 ;"heat to keep the";
1 ;"flask + contents every";
1 ;"finely it is divided, the";
1 ;"faster at the beginning of";
1 ;"experiment.)"
1 ;"exchange of energy."
1 ;"excess.)"
1 ;"equation for the reaction."
1 ;"empty.":
1 ;"effervescence to stop."
1 ;"direct reading bal-";
1 ;"dioxide)."
1 ;"deflagrating spoon.":
1 ;"deflagrating spoon was";
1 ;"crease the concentration of";
1 ;"cotton wool."
1 ;"contained in a balanced";
1 ;"contain energy?"
1 ;"constant all the time."
1 ;"chloric acid is used in each";
1 ;"chloric acid is the same at";
1 ;"chips into a conical";
1 ;"carbonate."
1 ;"carbonate, the faster the";
1 ;"burning produces enough";
1 ;"burn explosively, but";
1 ;"beaker."
1 ;"as much at the begin-";
1 ;"as it is used up."
1 ;"and water..."
1 ;"and stir.":
1 ;"and air..."
1 ;"and (s) are important."
1 ;"ance, and weigh it."
1 ;"amount of carbon dioxide";
1 ;"after the same amount of";
1 ;"acidic gas (sulphur";
1 ;"absorb heat from";
1 ;"a solid, because the par-";
1 ;"a piece of paper."
1 ;"Wind the tape (fast forward) to the end, turn it over, then...":
1 ;"When the sulphur";
1 ;"When the sulphur has";
1 ;"When the O-H bonds are formed, much more energy is released."
1 ;"When steam condenses into water,and water freezes into ice, the extra kinetic energy is"'"released."
1 ;"We started with sulphur";
1 ;"We started with salt";
1 ;"We could measure the";
1 ;"Volume of"'"sodium"'"thio-"'"sulphate":
1 ;"This is because the total";
1 ;"This is because the more";
1 ;"This is because the concen-";
1 ;"These may produce no change at all. Or they may cause:"
1 ;"There is more contact, and";
1 ;"Then as quickly as possible, oneafter the other:"
1 ;"The sulphur does not";
1 ;"The solid will grad-";
1 ;"The salt weighed just";
1 ;"The salt dissolves, but";
1 ;"The results will show that the higher the initial concentrationof sodium thiosulphate, the"'"faster the cross disappears."
1 ;"The rate of reaction is";
1 ;"The only energy"'"exchange involved"'"is the
1 ;"The mass of sulphur..."
1 ;"Swirl the liquid in the beaker, and put it down over the cross.":
1 ;"So although a change of mass"'"does occur, it is not absolute;"'"and overall, a
1 ;"Read the mass of the";
1 ;"Put a little common";
1 ;"Put 6.0 gm of marble";
1 ;"Put 50 cm
1 ;"Press any key to stop":
1 ;"Pour the liquid"'"into an evaporating"'"dish, and heat"'"gently until it has"'"all evaporated.":
1 ;"Pour some blue litmus";
1 ;"Pour in distilled water";
1 ;"Other chemical changes can be"'"accompanied by far more violent energy changes."
1 ;"Look down at the cross through the liquid. As soon as it dis- appears, stop the clock and"'"record the time.":
1 ;"Later it begins to burn";
1 ;"It would be difficult to recoverthe sulphur from the acid gas that remained."
1 ;"It will turn red, indicating"'"that the gas is acidic.":
1 ;"It will continue to burn after the heat is removed."
1 ;"It takes a large amount of"'"energy to break the two bonds ina water molecule."
1 ;"It is not possible to in-";
1 ;"In this program we will look at the first three factors."
1 ;"In order for a chemical reactionto occur, particles must collidewith each other. The higher the concentration of reactants, the more frequently the particles will collide."
1 ;"In fact the rate of a reaction is constantly changing.It has to be measured at a"'"particular instant."
1 ;"If, on balance, more energy is released when bonds are made"'"than absorbed when bonds are"'"broken, the reaction as a whole will release energy."
1 ;"If, in the second equation,";
1 ;"If the mass of this";
1 ;"Heat a little powdered";
1 ;"Gas and liquid molecules also move from place to place."
1 ;"First the sulphur melts";
1 ;"Energy is the capacity";
1 ;"EXOTHERMIC REACTIONS":
1 ;"ENDOTHERMIC REACTIONS":
1 ;"Draw a pencil cross on";
1 ;"Conversely, when the bonds are formed, a large amount of energyis released."
1 ;"But we cannot assume";
1 ;"But there will be a";
1 ;"But the H-H single bonds and theO=O double bonds have to be"'"broken first; and this requires energy."
1 ;"But if all the sulphur dioxide"'"gas was collected and weighed,"'"its mass would be found to be"'"greater than that of the"'"original sulphur."
1 ;"But how do";
1 ;"Although the white";
1 ;"Add 5 cm
1 ;"Actual experimental results willof course depend on the size of the beaker, how dark the cross is, etc."
1 ;"A white solid"'"remains: the salt"'"has reappeared in"'"its original form."
1 ;"A quantity of oxygen in";
1 ;"A mixture of hydrogen and oxygenwill explode if it is lit, but the gases will not react spon- taneously."
1 ;"= mass of sulphur dioxide"
1 ;"50 40 30 20 10":
1 ;"5 5 5 5 5":
1 ;"30 seconds for about";
1 ;"15 minutes."
1 ;"1 Particles collide more often"'" at higher temperatures because they are moving faster."
1 ;"00 05 10 15"
1 ;"0 10 20 30 40"
1 ;"...was reduced to";
1 ;"...it reappeared"'"when the water"'"evaporated."
1 ;"...as it did at"'"the end."
1 ;"...and ended up"'"with salt and water."
1 ;"...and ended up with an";
1 ;"+ contents,"
1 ;"* variations in temperature;":
1 ;"* variations in pressure;":
1 ;"* electric currents;":
1 ;"* contact with other sub-";
1 ;"* a physical change;":
1 ;"(The same amount of hydro-";
1 ;"(The calcium carbonate is in";
1 ;"(40 gm dm
1 ;"('2HCl' for example";
1 ;" "
1 ;" ":
1 ;"
1 , but we can say what it can
1 , and vice versa."
1 ), and start a";
1 ) using:":
1 ) into a";
1 (s) + 2HCl(aq)";
1 (other than
1 (g) = 1 mole hydrogen gas"
1 ''"When common salt dissolves in"'"water, a
1 ''"What is energy?"
1 ''"We will look at some experimentswhere changes take place.":
1 ''"We said at the beginning that"'"the study of chemical change"'"makes up a large part of chem-"'"istry."
1 ''"We could measure how long it"'"takes from start to finish."
1 ''"We can now summarise all these differences in the form of a"'"table."
1 ''"Use 10cm
1 ''"This is particularly true of"'"strong bonds:"
1 ''"This can also be explained in terms of the
1 ''"Therefore:":
1 ''"There are several important"'"differences between the two"'"kinds of change..."
1 ''"There are many different kinds of energy.":
1 ''"The units are normally moles perdm
1 ''"The symbol
1 ''"The shorter the time, the fasterthe rate."
1 ''"The results will show that the average speed of the reaction (and therefore the rate of the reaction at any particular mo- ment) increases the higher the temperature."
1 ''"The rate is usually measured by:"
1 ''"The next things must be done as fast as possible one after the other:"
1 ''"The experiment can be repeated at different temperatures, but with the initial concentration of sodium thiosulphate kept"'"constant."
1 ''"The effect of
1 ''"The commonest energy change in chemistry is when chemical ener-gy is converted into
1 ''"The amount of heat exchanged in a reaction is usually expressed either"
1 ''"Stop the clock when the cross disappears."
1 ''"Sometimes reactions need to be made as slow as possible. (Thinkof substances which decompose.)"
1 ''"Since considerable exchanges ofheat per mole often occur, the
1 ''"Repeat the experiment using"'"different amounts of sodium"'"thiosulphate solution:"
1 ''"Repeat the experiment over an initial temperature range of"'"20
1 ''"Remember the plug of cotton wooleach time.":
1 ''"Physical changes are generally
1 ''"Molecules, and the individual atoms within them, vibrate and rotate."
1 ''"Large energy changes occur when bonds are made or broken."
1 ''"It is difficult to say what"'"energy
1 ''"In industry time is money. The rate of a key reaction can be crucial. Scientists are always looking for ways to speed"'"reactions up."
1 ''"In a physical change,"'"
1 ''"How do we
1 ''"Even if the overall reaction"'"releases energy, bonds will haveto be broken to begin with."
1 ''"Energy will have to be supplied at the start of the reaction."
1 ''"Different reactions happen at different rates. Compare a fire-work with a rusting nail."
1 ''"Chemical energy stored"'"in substances can be"'"converted into heat and "'"light by burning;"
1 ''"Chemical changes are generally"'"
1 ''"Changes in bond energy are more important in chemistry than"'"changes in the kinetic energy ofparticles."
1 ''"By convention:":
1 ''"But this
1 ''"But it is not always easy to"'"measure a change in the concen- tration of a substance without interfering with the reaction."
1 ''"Bodies of any size, from planetsto tiny particles, can possess kinetic energy by virtue of"'"their
1 ''"An ideal measure is a physical property which varies with the concentration of a substance:"
1 ''"Adding water to make the volume of sodium thiosulphate solution up to 50cm
1 ''"A simple experiment can show howchanging the concentration of a reactant can change the rate of a reaction."
1 ''"A large part of chemistry is thestudy of chemical change."
1 ''"A body can also possess"'"potential energy by"'"virtue of its position."
1 '"then mass of carbon dioxide at t";
1 '"When sulphur burns in air, a"'"
1 '"When solutions of sodium thio- sulphate and dilute hydrochloricacid are mixed together they"'"react slowly to produce a milky precipitate of sulphur."
1 '"Warm the solution gently until the temperature is just above 20
1 '"Volume of"'"water":
1 '"Volume of"'"acid":
1 '"Time for"'"cross to"'"disappear":
1 '"This prevents acid spray escap- ing from the flask, which would distort the measurements."
1 '"This is
1 '"They are all interchangeable."
1 '"There are many ways of speeding up a reaction:"
1 '"The time taken to produce enoughsulphur to hide the cross is a measure of the
1 '"The results can be explained in terms of the
1 '"The next experiment gets closer to measuring the instantaneous rate of a reaction, rather than its average rate."
1 '"The mass decreases owing to the loss of carbon dioxide:"
1 '"Take the reaction of dilute"'"hydrochloric acid on calcium"'"carbonate."
1 '"So why do some reactions releaseenergy while others absorb it?"
1 '"So it is not surprising that"'"chemical changes of one kind or"'"another will be discussed in all"'"the other programs on this tape."
1 '"Repeat the experiment (
1 '"Plot the results on three graphsof
1 '"Once it is started the reaction may produce more than enough"'"energy for breaking other bonds."
1 '"Nowadays heat changes are"'"usually measured in
1 '"Most chemical reactions either produce heat or absorb it."
1 '"Lower the spoon into a gas jar.":
1 '"It is extremely difficult to"'"determine the total amount of"'"energy an amount of substance"'"possesses."
1 '"It is a simpler task to discoverthe
1 '"It could contain many different kinds of energy all at once."
1 '"In all chemical reactions, bondsare made
1 '"In a chemical change,"'"
1 '"Hydrogen will burn in oxygen to produce steam."
1 '"However, the faster the average speed, the faster will be the actual
1 '"How are they different?"
1 '"Discoveries can be made about the nature of elements, mixturesand compounds by subjecting themto changing conditions. These could be, for example:"
1 '"Conversely, a reaction can be slowed down by decreasing the concentration of reactants,"'"lowering the temperature, etc."
1 '"Calculate the total mass of car-bon dioxide produced (escaped) as at each 30 second interval:"
1 '"But if more energy is absorbed in breaking bonds than is freed in making them, the reaction as a whole will absorb energy."
1 '"At any moment the thickness of the precipitate will be a meas- ure of how far the reaction has progressed."
1 '"2 The collisions take place with more force: they are more"'" energetic."
1 '"(We could have"'"condensed the water"'"vapour and recovered"'"the distilled water.)"
1 '" In exothermic reactions,
1 '" In endothermic reactions,
1 '" 2HCl(aq) + CaCO
1 "u"+n,usr:
1 "s"+n,usr:
1 "i"+n,usr:
1 "'"of vaporisation"'"absorbed when the"'"water evaporates."
1 "'"(units of work)."
1 will only give a rough idea of the
1 when sub-"'"stances react together."
1 volume of liberated gas":
1 using a catalyst"
1 the solid";
1 the rate of a reaction?"
1 takes place."
1 raising the temperature":
1 powdered calcium carbonate"
1 per mole of reactant":
1 of water."
1 of the solution and 40cm
1 of sodium";
1 of dilute";
1 of 2M hydrochloric"'" acid."
1 mole nitrogen gas"
1 metallic bonds"
1 marble chips"
1 loss of weight."
1 light (only a minority of reactions are affected)."
1 is used to refer to the heat change that occurs in a reaction."
1 is far greater than the effect of
1 ionic bonds":
1 involved."
1 increasing the surface area of a solid reactant":
1 increasing the concentration of the reactants"
1 for the quantities";
1 ensures that the"'"total volume is kept constant."
1 distilled water)":
1 crushed marble chips"
1 covalent bonds":
1 colour change":
1 at any particular point."
1 The state symbols (g), (l)";
1 The more powdered the calcium";
1 The liquid in the beaker is";
1 The graphs are not straight";
1 The concentration of hydro-";
1 Stir the liquid with a"'" thermometer."
1 Start the stopclock."
1 Start a stopclock."
1 Read the temperature."
1 Put the flask on a";
1 Put the beaker on the cross."
1 Pour in 40 cm
1 Plug the neck with";
1 Each graph tends towards a";
1 Each chemical formula stands"'" for 1 mole:"
1 = mass of flask + con-";
1 = initial mass of flask";
1 6.0 gm of powdered calcium";
1 6.0 gm of partly crushed";
1 (litre) per second (mol dm
1 (kJ) is normally used (1 kJ = 1000 joules)."