S Matthew's Reaction Rates Experiment

INVESTIGATING THE RATE OF CHEMICAL REACTIONS Introduction: According to the collision theory for a chemical reaction to occur, the reacting species must collide with the proper orientation and the collision must be energetic enough so that the electron clouds of the colliding particles interpenetrate with each other. At this moment the particles are forming an activated complex: they have reached the transition state (the most energetic possible state).After this, two species separate that can be either the original particles or two completely new particles with different properties. Chemical bonds have been re-located and a chemical change has occurred. Generally, we cannot control the orientation of the colliding particles (although in some cases we orient the particles to react as we wish) but we can promote the number of collisions per second and the energy of the colliding species. We can do so, increasing the concentration (number of particles per unit volume) of the reactants, increasing the contact area when the reactants are in two different phases, or increasing the temperature (i. e. a solid and a liquid or two immiscible liquids). An increase in temperature will increase the number of collisions but the most important fact is that collisions will be more energetic. All these facts contribute to an increase of successful collisions and as a consequence the reaction will go faster. Obviously we can act in the opposite direction and force the reaction to proceed at a slower pace. In these experiments you will study the effect of changing the surface area and the temperature in the rate at which an antacid tablet dissolves in water. Aims: To study the effect of changing temperature and surface area in the rate at which an antacid tablet dissolves in water. Antacid tablets contain both a weak acid and sodium bicarbonate (also called sodium hydrogenocarbonate). As soon as the tablet dissolves, the acid will decompose the bicarb releasing CO2 bubbles. The chemical reaction (decomposition of bicarb in acidic medium) will be completed as soon as the tablet has dissolved. EXPERIMENT 1: THE EFFECT OF TEMPERATURE ON RATE Apparatus: Two 250 mL beakers, four antacid tablets, mortar and pestle, thermometer, buirner, tripod, wire gauze, stopwatch, ice cubes, graph paper. Procedure A. Hot water 1- Fill the beaker with to 200 mL of water. 2- Heat the water to 70ºC - 72ºC. Control temperature with the thermometer 3- Drop 1 whole Alka-Seltzer tablet into the water. 4- Simultaneously start the stopwatch 5- Stop the stopwatch as soon as the bubbling ceases. 6- Record your result to the next tenth of a second.

B. Warm water 123456-

Fill the beaker with to 200 mL of water. Heat the water to 50ºC - 52ºC. Control temperature with the thermometer Drop 1 whole Alka-Seltzer tablet into the water. Simultaneously start the stopwatch Stop the stopwatch as soon as the bubbling ceases. Record your result to the next tenth of a second.

C. Tap water 123456-

Fill the beaker with to 200 mL of water. Control temperature with the thermometer Drop 1 whole Alka-Seltzer tablet into the water. Simultaneously start the stopwatch Stop the stopwatch as soon as the bubbling ceases. Record your result to the next tenth of a second.

C. Chilled water 123456-

Fill the beaker with iced water to 200 mL of water. Control temperature with the thermometer Drop 1 whole Alka-Seltzer tablet into the water. Simultaneously start the stopwatch Stop the stopwatch as soon as the bubbling ceases. Record your result to the next tenth of a second.

Experiment Nr 1 2 3 4

Temperature (ºC) Time (seconds)

Graph your data points (water temperature vs. time to fully dissolve) to show the effect of temperature on Rate of Reaction. EXPERIMENT 2: THE EFFECT OF INCREASING CONTACT AREA ON RATE Apparatus: Two 250 mL beakers, three antacid tablets, mortar and pestle, stopwatch

Procedure A. Whole Tablet 12345-

Fill a beaker with exactly 200 mL. of room temperature water. Drop 1 whole Alka-Seltzer tablet into the water. Simultaneously start the stopwatch Stop the stopwatch as soon as the bubbling ceases. Write down your result to the next tenth of a second.

B. Tablet Broken into 8 Pieces 1- Fill a beaker with exactly 200 mL of room temperature water. 2- Place 1 antacid tablet onto a sheet of paper and break into approximately 8 pieces of about equal size. 3- Slide the broken tablet into the water. 4- Simultaneously start the stopwatch 5- Stop the stopwatch as soon as the bubbling ceases. 6- Write down your result to the next tenth of a second. C. Powdered Tablet 123456-

Place the antacid tablet into mortar and grind to a fine powder. Transfer powder into a dry beaker. Add 200 mL of water to the beaker. Simultaneously start the stopwatch Stop the stopwatch as soon as the bubbling ceases. Write down your result to the next tenth of a second.

Time for reaction to be completed Whole Tablet _________ Seconds 8 Pieces _________Seconds Powder _________Seconds 1. As particle size decreases, the total surface area of a reactant ________________. As a result, the probability of collisions between particles ________________, and the rate of reaction ___________________. 2. Particle size appears to have _______________ (less or more) of an effect on the rate of reaction than temperature.