• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month
Page
  1. 1
    1
  2. 2
    2
  3. 3
    3
  4. 4
    4
  5. 5
    5
  6. 6
    6
  7. 7
    7
  8. 8
    8
  9. 9
    9
  10. 10
    10
  11. 11
    11
  12. 12
    12
  13. 13
    13
  14. 14
    14
  15. 15
    15
  16. 16
    16
  17. 17
    17

Determine the rate equation for the reaction of hydrochloric acid with magnesium metal, and find the activation energy for the reaction: 2HCl(aq) + Mg(s) à MgCl2(aq) + H2(g).

Extracts from this document...

Introduction

Order of reaction - Concentration Problem The problem is to determine the rate equation for the reaction of hydrochloric acid with magnesium metal, and find the activation energy for the reaction: 2HCl(aq) + Mg(s) --> MgCl2(aq) + H2(g) Background Information Rate of reaction is the change in concentration of a reactant or product with respect to time as the reaction progresses. Particles react when they come into contact with each other with sufficient kinetic energy. This amount of energy is called the activation energy of the reaction. For my experiment I define rate as the change in concentration of hydrochloric acid per second. The rate of a reaction is affected by four factors.1 1. Concentration is the number of particles of a substance per unit volume. The higher the concentration, the greater the chance of a collision between reactants. 2. For a heterogeneous reaction, where reactants are in different physical states, the reaction takes place on the interface between the reactants. Therefore the surface area of the interface is a factor. The greater the surface area, the higher the chance of there being collisions between reactant particles. 3. Rates of reaction are dependent on temperature. Reactant particles are constantly moving randomly and colliding in ways that may break or form bonds. Increasing temperature increases the kinetic energy these particles have, so at higher temperature they move faster, which increases the force with which they collide, making a reaction more likely. 4. For a certain reaction, there may be a catalyst that works by providing an alternative reaction route with a lower activation energy. This means that under the same conditions more particles will have the necessary activation energy to react, and the rate of reaction will be higher. Method The initial rate of the reaction between magnesium and hydrochloric acid was measured for a range of concentrations of hydrochloric acid. The first method I used was to measure the volume of hydrogen gas produced in the first 10 seconds of the reaction. ...read more.

Middle

If consecutive half-lives are constant, then the reaction is of 1st order. If the consecutive half-lives are increasing, then the reaction is 2nd order or greater. As shown on the graph of time against concentration, the consecutive half-lives (t1=15s, t2=29s, t3=54s) for my experiment are increasing. Therefore I must use a different method for determining the order of reaction. Logarithms involving concentration and reaction rate can be used to produce a graph from which we can work out the order and rate constant of reaction. Rate = k[HCl]n , where k is the rate constant, and n is the order of the reaction. If we take the logarithm of both sides of this equation then we get: log rate = n log[HCl] + log k . In the graph below of log[HCl] vs. log(rate), the gradient of the line produced will be the order of the reaction, and the y-intercept will be the logarithm of the rate constant. From this graph the order of the reaction is 1.98 and the rate constant is 100.426 = 2.67 mol-1 dm3 s. 1.98 is sufficiently close to 2 for me to draw the conclusion that the reaction is of 2nd order with respect to concentration of HCl, since there are significant sources of error in my experiment. Sources of error The reaction between HCl and magnesium is exothermic. This means that as the reaction proceeds, heat is produced. Temperature is a factor affecting the rate of reaction: the rate is faster as temperature increases. This means that despite my efforts to make the experiment a fair test, concentration was not the only factor influencing my results, there was also the increasing temperature of the reaction mixture. I repeated the experiment twice more to measure the temperature increase. The mixture went from 23�C to 30�C and 31�C on each test. From the results of the second part of this investigation, we can estimate the error as a factor of the rate. Using the Arrhenius equation, k = Ae-Ea/RT. ...read more.

Conclusion

The main source of error however is judging when the reaction is complete. As the reaction progresses, there is less and less visual activity, until suddenly there is no magnesium left. It is difficult to judge exactly when that point is. Therefore I estimate that on any of my tests there could be an error of up to �2 seconds. As well as being heated up by the exothermic nature of the reaction, the reaction mixture will cool down as the reaction proceeds if it is at a temperature higher than that of its surroundings. This would have affected my results much more than the heat produced by the reaction, as the volume of HCl was very large. Therefore my results must be inaccurate due to the reduction in rate of reaction due to the falling temperature of the reactants at starting temperatures. Limitations More accurate readings would have been obtained if I was able to control the change in temperature over the course of the reaction. This would be possible if I could place the beaker in which the reaction takes place inside a water bath which is maintained at the desired temperature for the reaction. The water bath would receive some of the heat produced by the exothermic reaction, and also it would warm up the reaction mixture as if its temperature falls. Ideally the water bath should be large, for maximum heat capacity, and the reaction mixture small, to allow maximum heat exchange. Visually judging when the reaction is complete is a method that always has a margin of error due to human error. This was estimated at about �2 seconds. I could have instead timed how long it took the reaction to produce a certain amount of hydrogen gas, say 50cm3, and taken the inverse of this time to find a rate. This would eliminate the problem of being uncertain when to stop the stopwatch. 1 Nuffield Advanced Chemistry, Students Book p242. 2 Nuffield Advancing Chemistry website: www.chemistry-react.org/go/Tutorial/Tutorial_4425.html 3 Nuffield Advanced Chemistry Student Book, p257 Hubert Rogers - 1 - Candidate No: 4484 ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our GCSE Patterns of Behaviour section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related GCSE Patterns of Behaviour essays

  1. Marked by a teacher

    The Effect of Concentration on the Rate of Reaction between Magnesium [Mg] and Hydrochloric ...

    4 star(s)

    Many reactions are not successful only some are successful and this is because some reactions have collisions in which the molecules are moving around giving the bonds the strength to break (activation energy). If you increase the concentration of the reactions and the temperature it brings more collision and therefore the success rate is higher increasing the rate of reaction.

  2. Marked by a teacher

    Investigation of the rate of reaction between Magnesium and Hydrochloric acid

    4 star(s)

    We will use this as this measuring cylinder would be more accurate as the readings are in 0.5ml. Relating to the measuring cylinder, we will use 50ml of acid, therefore we will be using the measuring cylinder twice. I will also use a stopwatch to record the time of how much gas has been made.

  1. Marked by a teacher

    How dose temperature affect the rate of reaction between magnesium and hydrochloric acid.

    3 star(s)

    The first, precipitation method was not suitable, the reaction that we are looking at is not a precipitation reaction it is an exothermic one, a precipitation reaction is usually between two liquids. Water bath will be needed for safety and to keep the acid at needed temperature, so the second and third method would be too complicated.

  2. Marked by a teacher

    Rates of reaction between hydrochloric acid and magnesium

    3 star(s)

    It is shiny, lightweight and ductile. It tarnishes slightly when exposed to air and because of this magnesium is protected by a thin layer of oxide that is fairly impermeable and difficult to remove. Magnesium is a highly flammable metal when in thin strips or in powder form.

  1. Marked by a teacher

    For my experiment I am finding out the effects on the reaction rate when ...

    3 star(s)

    > Delivery tube- to get the hydrogen from the conical flask into the burette filled with water to measure the amount of hydrogen gas produced. > Stand with a burette clamp- A burette has a small base and is very tall so a stand and a burette clamp is needed

  2. Marked by a teacher

    The aim of this investigation is to investigate the rate of reaction of magnesium ...

    and add it to the water. * Place the side arm tube in a water bath at 20OC, set up the apparatus below. * Measure 10.9 cm of magnesium ribbon and check on the balance that it weighs 0.1g. * Coil the ribbon around a pencil and then drop it into the side arm tube and

  1. Investigating the Effect of Different Concentration Of Acid Rain On The Rate Of Reaction ...

    lower chance of a collision and therefore a successful collision and this then results in the rate of reaction being decreased which will make the results inaccurate. However probability in theory would show that it is likely that the number of times which I get a surface area which is

  2. RATE OF REACTION

    This is because the potato should fully submerge, by having total contact with the solution. When using the scales, we will make sure that the scale is reading zero before we put the potato pieces on it. This is so that we don't get a false reading, with the weight of our potato with the reading it had before.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work