Faster Rate Of Reaction example essay topic

Planning Aim! V To investigate the effect of concentration on the rate of reaction between marble chips and excess hydrochloric acid. Introduction Rate Of Reaction Reactions can either be slow or fast. For example, for concrete to set, it takes two to three days. However, when solutions of silver nitrate and sodium chloride are mixed, a precipitate is formed very quickly. Rate is defined as the!

SS measure of change that happens in a single unit of time!" . Measuring exactly how fast a reaction is can be very useful; in a factory, the chemical engineers need to know exactly how fast each reaction is, and how long it takes to complete. They need to find the reaction's rate. Firstly, what happens when a reaction takes place?

When an acid is added to a reactant, a reaction takes place. The particles in the acid move around continuously. For this reaction to take place, the acid particles must collide with the reactant with enough energy to form a product. Acid Particle Water Molecule Reactant Acid particle If the collision does not have enough energy, no reaction occurs, and the acid particle bounces away again; no product is formed. The rate of a reaction depends on how many successful collisions there are in a given unit of time. There exist different factors that affect the rate of a reaction: -temperature If the temperature is increased, the particles have more energy, move faster, and thus collide faster, and with more force.

This increases the rate of a reaction. -concentration The more the concentration of an acid, the faster the reaction will be, since there are more acid particles to collide and react with the reactant. -surface area of a solid reactant Using a reactant with more surface area will result in a faster rate of reaction! V when the reactant is powdered, many more of its atoms are exposed, and thus there is a greater chance of successful collisions. -catalyst In the presence of a catalyst, a collision needs less energy to be successful. More collisions become successful in the presence of a catalyst, and thus the rate of reaction increases. The catalyst does not get used up at all, and can be used over and over again.

The Concentration Factor If the concentration of an acid is increased, the reaction goes faster. In a dilute acid, there are more water molecules than acid particles. This means that the chances of an acid particle hitting the reactant are very slight. However, in a more concentrated acid, there are more acid particles, and thus there are more chances of it hitting the reactant's particles successfully. The more successful collisions there are, the faster the reaction is. In a successful collision, bonds are broken, and new bonds are formed.

In this coursework, I will only be investigating this factor, and prove how it affects the rate of reaction. The reaction that I will be investigating is the reaction between calcium carbonate (in the form of marble chips) and hydrochloric acid: CaCO + 2 HCl "^3 CaCl + 2 H O + CO There are different ways in which I can measure the rate of a reaction, for example - the top pan balance method: In which I can decipher the rate of the reaction by noting how much mass is lost in a certain amount of time. - the syringe method: In which I can decipher the rate of the reaction by noting how much gas I can collect in a gas syringe in a certain amount of time When I place calcium carbonate chips into a beaker of hydrochloric acid, the HCl particles that constantly mover around collide with the calcium carbonate chips. If the collision has sufficient energy, then a reaction takes place, and products are formed, i.e. calcium chloride, water and carbon dioxide. In theory, if I increase the concentration of the acid, then the rate of the reaction should increase, and if I use a dilute acid, then the rate of the reaction should decrease.

This is what I plan to investigate by carrying out an experiment in which I can see how the concentration of the hydrochloric acid affects the rate of the reaction. In dilute Hydrochloric acid, there is not much chance of a collision occuring: If I double the concentration, the chances of a successful collision are doubled: If I triple the concentration, the chances of a successful collision are also tripled. Thus, when the concentration is doubled, the rate of reaction is also doubled, and when the concentration of acid is tripled, then the rate of reaction is also tripled, and so on. However, certain factors that also affect the rate of a reaction also need to be kept constant, so that we can be sure that it is only the change in concentration that affects the rate of the reaction, and not any other factor: -temperature "^3 remains constant -surface area of calcium carbonate "^3 remains the same -catalyst "^3 none used Calculations: 1. To obtain 100 cm 3 of carbon dioxide, I need to calculate how much calcium carbonate I will need to use: CaCO + 2 HCl "^3 CaCl + 2 H O + CO 1 mole of calcium carbonate "^3 1 mole of carbon dioxide 100 gms of calcium carbonate "^3 24,000 cm 3 of carbon dioxide x "^3 100 cm 3 of carbon dioxide x = 100 100 / 24,000 = 0.4166666666!

K = 0.42 gms of calcium carbonate is needed to produce 100 cm 3 of carbon dioxide. 2. I will be using 5 different concentrations of hydrochloric acid. 3. The volume of acid that I take will remain the same. Method: - Apparatus Gas syringe Stand Conical Flask (in which reaction will be carried out) Measuring Cylinder (with which acid will be measured) Funnel (to aid in pouring acid if the container mouth is wide) Weighing Balance Tongs (to aid in lowering calcium carbonate into the conical flask) Bung (to cork the conical flask and make sure that the carbon dioxide produces does not escape) Stopwatch (to time the reaction so as to find out the rate of the reaction) Procedure: Plunger can move out Gas syringe Bung Glass wall divides flask in two Stop clock I will set up my apparatus as shown in the figure above.

The flask is divided in two; I will put calcium carbonate chips in one part, and hydrochloric acid in the other part. When I am ready, I will tip the flask to let the two reactants mix, and I will start the clock at the same time. As the reaction takes place, carbon dioxide is produces, and will be collected in the gas syringe. As the gas enters the syringe, the plunger is forced out. I will note the volume of gas collected at intervals of 15 seconds. Thus I will get values which I can note in the following table: Time (seconds) Volume of Carbon Dioxide (cm 3) First reading Second reading Average Expected Graph: I expect my graph will turn out this way because the reaction is always fastest at the beginning of the experiment.

This is because, at the start of the experiment, there are plenty of acid particles and calcium carbonate particles. But these get used up during successful collisions. After some time, there are fewer calcium carbonate atoms, and the acid is less concentrated. Thus the reaction slows down. The curve becomes less steep because of the decrease in the speed of the reaction.

My curve gets flat after this; this indicates that the reaction is over, and that the reactants are used up.