Different reactions Essay Example for Free

Different reactions Essay How quickly a reaction happens is called the rate of reaction. Chemical reactions take place when two or more chemicals react with one another by colliding with each other. The increase in temperature increases the amount of collisions between particles, this fastens the reaction. If a reaction has a low rate that means the molecules combine at a slower speed than a reaction with a high rate. Particles need a minimum amount of kinetic movement if they are going to react when they collide. This is known as Activation energy. The collision theory is the idea that different reactions happen at different rates. Reactions that occur slowly have a lower rate of reaction. Fast reactions are due to an increase of collisions; slow reactions are due to decrease in collisions. Reactions that happen quickly have a high rate of reaction (e. g. explosions). Concentration: The concentration of a solution is how strong the solution is. A stronger acid contains more acid particles and less water particles than a weaker acid. Increasing the concentration of a solution leads to more collisions (greater frequency of collisions) so the rate of the reaction goes up. With a more concentrated acid, the number of acid particles is greater, so the number of collisions is greater and the rate of the reaction is higher (faster. ) Changing the concentration of the acid does not change how quickly the particles are moving (i. e. it doesnt increase the amount of energy they have. ) Temperature: When we increase the temperature at which a reaction is taking place, the particles move more quickly. At a lower temperature, the number of collisions is lower because the particles are moving more slowly. Also when a collision occurs, there is less chance of a reaction taking place because the movement energy in the particles is less. At a higher temperature, the number of collisions is greater because the particles are moving more quickly. When a collision occurs, there is more chance of a reaction taking place because the movement energy in the particles is greater. Gas pressure: Pressure affects the rate of reaction, especially when you look at gases. When you increase the pressure, the molecules have less space in which they can move. That greater concentration of molecules increases the number of collisions. When you decrease the pressure, molecules dont hit each other as often. The lower pressure decreases the rate of reaction. (2) Catalyst: Different catalysts speed up different reactions. The table shows some common catalysts: A catalyst provides a surface on which the reaction can take place. This increases the number of collisions between the particles of the substances that are reacting. A catalyst lowers the activation energy (the minimum amount of energy needed for a reaction to take place). This means that the particles can react with less energy than they needed before the catalyst was added. (3) Surface area of particles: By increasing the surface area of the reactants, there are a higher number of reaction sites. Reaction sites are specific sites on molecules at which reactions occur. Increasing the number of reaction sites increases the number of total collisions. The greater the frequency of total collisions, the greater the frequency of e.ffective collisions. If the frequency of effective collisions increases, so does the reaction rate. Introduction/Aim. In this investigation, I am finding out how concentration affects the rate of reaction between Hydrochloric acid and Sodium Thiosulphate. I am going to measure the rate of reaction when hydrochloric acid is added to sodium thiosulfate. When sodium thiosulfate and Hydrochloric Acid are mixed, a yellow precipitate of sulphur is produced. The solution becomes increasingly difficult to see through as more and more sulphur is formed. This is how I plan to measure the rate of reaction. I will place a paper with a black cross underneath the solution and will stop the clock when the cross can no longer be seen. I will find out the answer by doing a preliminary test to experiment this, I will then compare and discuss the results in my evaluation then I will also state how this experiment I done could be improved, in my conclusion. But before doing the real experiment I will carry out a preliminary test. What is a Preliminary test? This is a test that is done before the real test. It gives an idea of the real thing; through the test you can make changes to make sure the real one is fair and reliable e. g. changing equipment or concentration of sodium thiosulfate solution. A preliminary test is more of a trial than an experiment – to find out if the equipment/method or even experiment works. A preliminary test is generally a baseline for further testing and development. It helps you refine ideas and change key concepts of the experiment. Prediction: Knowing the information above, I predict that as the concentration of the Sodium Thiosulphate increases, the rate of reaction will also increase. This means that the rate/concentration graph I compile from my experiments results will have a positive correlation. I believe this will happen because, according to the collision theory, as the concentration of a solution is increased the number of particles inside the solution increases. If the number of particles inside the solution is increased it makes collisions with reacting particles more likely. Also, I believe that the time/concentration graph will have a negative correlation because if my prediction is true, as the concentration increases the time taken for the reaction to take place will decrease. Preliminary Experiment: I did a preliminary experiment to get used to the sequence of events. I got to know all the apparatus and the method. Word Equation for the reaction: Sodium Thiosulfate + Hydrochloric acid Sodium Chloride + Sulphur + sulphur dioxide + water Ionic equation for reaction: 2Na+ + S2O32- + 2H+ + 2Cl- 2Na+ + 2Cl- + SO2 (g) + S + H2O (l) Balanced Symbol Equation for the reaction: Products Reactants Na2S203 (aq) + 2HCl (aq) 2NaCl (aq) + S (s) +SO2 (g) +H20 (l) I only did the experiment one, not three times so I did not get an average time for each concentration. I made sure the volume of Sodium Thiosulfate solution each time equalled to 10cm3 . The one thing I kept consistent was 10cm3 of Hydrochloric acid. I varied the concentration of the Sodium Thiosulfate and water. Below is a results table for my preliminary experiment. Preliminary Table Volume of water (cm3) Volume of Sodium Thiosulfate (cm3) Concentration (M) Volume of Hydrochloric Acid (cm3) Concentration (M) Time taken (seconds)Â   Preliminary method: 1. If you have not already done so, put on your goggles and gloves. 2. Place the paper with an X onto a flat surface and put a conical flask on top. 3. Measure 9 cm3 of sodium thiosulphate using a pipette and put it into a flask. Then measure 1 cm3 of water using a different pipet. 4. Then measure 10 cm3 of hydrochloric acid using a measuring cylinder. 5. Add first the acid then water and place a ball of cotton wool on top of the flask to block the formed gas from getting into the air. When acid and water is added, immediately start the timer. 6. Look down at the cross from above the flask. When the cross disappears, stop the timer and note the time, recording it in the table. 7. Repeat this process using different concentrations of sodium thiosulpahte solution with water as shown in the table above. 8. Carefully pour the solution into the sink straight after each test. Preliminary Safety: Safety is a key aspect to any experiment. There are a lot of safety issues we must abide when performing this experiment. A key safety aspect was that we covered the top of the conical flask with cotton wool, making sure no gas escapes the air we breathe into as sulphur dioxide; one of the products formed from the experiment is a toxic gas. I also decided to wear goggles to protect my eyes from the acid splashing, squirting or any way entering my eye. Also be sure to tie hair back because if the sodium thiosulphate makes contact with my hair it could dye it blonde (bleach it) or if it comes into contact with my skin it would turn white and peel off. Another precaution to take measure of is wearing gloves to protect your skin as hydrochloric acid is corrosive. Afterwards, when you have done your experiment thoroughly wash away all apparatus used and pour the solution down the sink. Apparatus: 1. Sodium Thiosulphate solution – (This is the variable factor being studied in the reaction) 1. Hydrochloric Acid 2. Water 3. Conical Flask – (to put both the hydrochloric acid and sodium thiosulphate into. ) 4. 3 Pipettes – (one for the hydrochloric acid and one for the sodium thiosulphate and one for water; this allows you to easily transfer the liquids. ) 5. Cotton – (this blocks the top of the conical flask to make sure sulphur dioxide the toxic gas produced doesn’t escape. ) 6. A paper marked with an x – (to be certain when to stop the timer. ) 7. Stop watch/Timer – (to stop the time when ‘X’ is not visible. ) 8. Goggles – (to protect your eyes from acid entering the eyes – for safety measurements. ) 9. Gloves – (protects your skin from hydrochloric acid; corrosive. ) 10. 2 Measuring cylinders’ (to measure the volume of the acids. ) Prediction: I predict that the greater the concentration of Sodium Thiosulfate Solution, the faster the chemical reaction will take place. Therefore, the cross will disappear more quickly due to the cloudiness of the solution. If solutions of reacting particles are made to be more concentrated, there are a higher number of particles reacting. Meaning collisions between Hydrochloric Acid and Sodium Thiosulfate Solution are more likely to occur. All this can be justified by the full understanding of the collision theory itself: For a reaction to occur particles have to collide with each other. Only a small per cent result in a reaction. This is due to the energy barrier to overcome. Only particles with enough energy to overcome the barrier will react after colliding. The minimum energy that a particle must have to overcome the barrier is called the activation energy, or Ea.