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REACTION RATES BY HALEY ROSALEZ AND NIKKI STEVENS

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EXAMPLES OF REACTION RATES Here are just a few everyday demonstrations that temperature changes the rate of chemical reactions: *Cookies bake faster at higher temps. *Bread dough rises more quickly in a warm place than a cool place. *Low body temperature slows down metabolism. In fact, warm-blooded animals regulate body temperature so that their bio-chemical reactions run in the correct rate. Light-sticks produce light via a chemical reaction. Dropping a light-stick into hot water makes it glow more intensely, demonstrating that the reaction runs faster at higher temps. Increasing the concentration of reactants also changes reaction rates: Two antacid tablets will neutralize a given amount of acid faster than one tablet will. Higher concentrations of acid in rain erode marble faster than lower concentrations.

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Reaction rates : The change in concentration of a reactant or a product with time. We calculate the average rate of a reaction over a time interval by dividing the change in concentration over that time period by the time interval for the change in concentration of an reactant. The equation (where the brackets means concentration) is: Rate = [ reactant at t2]-[ reactant t1] t2 – t1 We use the minus sign before the ratio in the previous equation because a rate is a positive number. We do not need the minus sign when calculating average rates from products. Rate =[ reactant] or rate = [ product] t t REACTION RATES

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REACTION RATE GRAPH GRAPH In order to determine the rate law of reaction from a set of data consisting of concentration versus time, three graphs need to be made. Each graph is linear. [a] versus t ( Linear for a zero ) In [a] versus t (linear for a 1 st order reaction) 1/[a] versus t (linear for a 2 nd order reaction)

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REACTION RATE QUIZ 1.What is the definition of reaction rates? 2.What is the equation where the brackets mean concentration? 3.Why do we use the minus sign before the ratio in the previous equation that was shown in slide 3? 4.What are a few everyday demonstrations that temperature changes the rate of chemical reaction? 5.What chemical do light sticks produce? 6.How do you determine the rate of law from a set of data? 7.What is the equation for reaction rates? 8. true or false One antacid will neutralize a given amount of acid as equally as two tablets will. 9.True or false Cookies bake faster at higher temperature. 10.True or false Low body temperature slows down metabolism.

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ANSWER KEY 1.The definition of reaction rates is the change in concentration of a reactant or a product with time. 2.Rate = [ reactant at t2] – [reactant t1 ]/t2-t1 3.We use the minus sign before the ratio before the ratio in the previous equation because a rate is a positive number. 4. Cookies bake at higher temps, light sticks produce light via a chemical reaction. 5. They produce the chemical light via. 6.In order to determine the rate law of reaction from a set of data consisting of concentration versus time three graphs need to be made each graph is linear. 7. Rate =[reactant]/t or [product]/t 8. False 9. True 10. False

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REACTION RATE WEBSITES en.wikipedia.org/wiki/Rate_equation www.purdue/chem.com

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