Worksheet Reaction Rates Answer Key

Name: ___________________________ Grade: ________   Objective: Use the collision theory to deduce why a reaction’s rate changes when temperature, pressure, surface area, concentration and catalyst are changed. Interpret and label energy diagrams. 1. A study of reaction rate is called chemical kinetic. 2. Reaction rate refers to how quickly or slowly the reactants disappear and the products appear. It is measured in terms of the energy of the reactants. 3. If a reaction is to occur, reacting particles must first collide and this collision must be effective. 4. What are the five major factors that affect reaction rate? Pressure, temperature, concentration, catalyst, and surface area. 5. Why would a mixture of gases react faster when the volume they occupy is decreased? There will be less space for the particles to move therefore the amount of collisions between the gas particles will increase. 6. Why would iron fillings rust faster than an iron nail? The iron fillings have a larger surface area than the iron nail therefore the amout of collisions between air particles and iron will be greater. 7. What is the effect of a catalyst on the required energy to achieve effective collisions? A catalyst will lower the activation energy of the reaction. 8. Enzymes act as catalysts in our bodies. Have you ever noticed that your hands seem to get “stiff” when they get cold? The reason is that these enzyme reactions causing the muscles to contract slow down when your hands are cold so you can’t contract you muscles as fast and your hands feel stiff! Decreasing temperature decreases the rate of reaction. 9.Enzymes are in molds and bacteria that spoil food. Explain using your knowledge of factors affecting the rate of reaction, why food doesn’t spoil as fast when it is refrigerated as it would at room temperature. When food is refrigerated the temperature drop causing the particles to slow down and decreasing the amount of collisions between particles, thus decreasing the rate of the spoilage for the food. 10. Due to decomposition reactions with oxygen or carbon dioxide in the air, meat begins to feel slimy and smell spoiled. Explain using your knowledge of chemical kinetics, why meat spoils less rapidly if left unsliced. Is left unsliced food will have a smaller surface area and will have less collisions between it and the air particles therefore decreasing the rate of the reaction. 11. Based on your knowledge of factors affecting the rate of reaction, why is there a danger of explosions in places such as silos and coal mines where there are large quantities of powdered, combustible materials? Powdered substances have a greater surface area therefore will increase the possible collisions. C6H12O6 (S) + 6 O2 (g)  12.Use this reaction for the questions below: 6 H2O (g) + 6 CO2 (g) a. What happens to the concentrations of the reactants and products as the reaction proceeds in the forward direction? The concentration of the reactants decrease, while the concentration of the products increase. b. According to the collision theory, what two conditions are needed for the reactants to react? Proper orientation, and enough energy. c. What is activation energy for a chemical reaction? Minimum amount of energy needed for the reaction to take place. d. Fill the table below. Change in condition: Does this increase or decrease the rate of reaction? Explain why Increasing the temperature Increase Particles will have more energy which will increase the amount of collisions Increasing the concentration of C6H12O6 Increase There will be more particles present which will increase the number of collisions Decreasing the concentration of O2 Decrease There will be fewer particles which will decrease the number of particles Increasing the surface are by chewing up food in your mouth Increase There will be more possible surface for collisions Decreasing temperature Decrease Particles will be less energetic which will decrease the number of collisions Increasing pressure in the container Increase The volume of the container will be smaller therefore there won’t be enough space for the particles to move which will cause more collisions Decreasing the concentration of H2O Nothing H2O is a product it doesn’t have any effect Increasing the volume of the container the reaction occurs in Decrease The volume of the container will be greater therefore there will be too much space for the particles to move which will cause less collisions Increasing the concentration of CO2 Nothing CO2 is a product it doesn’t have any effect Using a catalyst Increase It lowers the activation energy of the reaction 13. Use the following diagram to solve the next questions: a.c. P R a. Label the diagram with the following terms: reactants, products and activated complex. b. Draw and label what this diagram would look like if a catalyst was added to the reaction. c. How much energy do the reactants have? 20 kJ/mol d. How much energy do the products have? 35 kJ/mol e. How much energy is required to activate this un-catalyzed reaction? 45 kJ/mol f. Is this reaction endothermic or exothermic? How do you know? Endothermic. ER < EP 14. Using the energy curve below label and answer the following question. Ea.c. Ea Ea ’  ER E EP a. It is a/an exothermic reaction and energy is released. b. Draw a line segment that represents the energy of the reactants and label the line. c. Draw a line segment that represents the activation energy of the forward reaction and label the line. d. Label where the activated complex occurs and draw a line segment that represents the energy of the activated complex. e. Draw a line segment that represents the energy of the products and label the line. g. Draw a line segment that represents the  f. Draw a line segment that represents the activation energy of the reverse reaction and label the line. H of the reaction and label the line. h. What is the value of the energy of the reactants? 40 kJ/mol i. What is the value of the energy of the products? 10 kJ/mol k. . What is the value of the  j. What is the value of the energy of the activated complex? 58 kJ/mol H reaction? 30 kJ/mol