Chemical Reactions ( Aju Varghese)
Title: Rates of Reactions
Principle Investigated: Effect of temperature on the rate of a chemical reaction.
Standards:
HS-PS1-5: Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs.This is explained based on the collision theory.
SEP3: Planning and carrying out investigation. Students will be planning and carrying out the investigation about how the rate of the reaction changes with change in temperature of the reactants.
Crosscutting Concept7: Stability and Change Rate of change, in this case the production of CO2 can be quantified and modeled.
SEP4: Analyzing and interpreting data.
Materials :
Masking tape, cups, hot and cold tap water, a thermometer, effervescent antacid tablets (Alka-Seltzer), a stopwatch to record time, a paper and pen or a computer/smart phone to record data.
Procedure:
1. Mark the letters A and B on separate pieces of masking tape. Label each cup with one of the lettered pieces of tape.
2. Fill each cup half full of water as follows: (A) cold tap water (B) Hot tap water
3. Measure and record the temperature of water in cup A.
4. Drop a tablet into cup A and measure the time it takes for the reaction (bubble production) to end. Repeat steps 3 and 4 using cup B.
Student prior knowledge: Students should have a basic understanding of atoms and molecules, and chemical reactions.
Explanation: The rate of a chemical reaction depends on the temperature, concentration, particle size and the use of a catalyst. Collision theory helps us understand why changing one of these factors ( in our experiment changing the temperature ) affects the rate of a chemical reaction.
Increasing the temperature increases both the frequency of collisions and the number of particles that have enough kinetic energy to slip over the activation-energy barrier to become products. An increase in temperature therefore causes products to form faster.
The chemical reaction that occurs when Alka-Seltzer tablet is dropped in water is as follows:
3NaHCO3 + C6H8O7 -----> Na3C6H5O7 + 3H2O + 3CO2
Questions & Answers:
1. Does every collision between reacting particles lead to products?
No, the collision must have sufficient energy to break and form bonds.
2. Will changing the temperature of the reactants change the activation energy of the reaction?
No, It will only increase the number of reactants having activation energy needed to react.
3. What do you predict concerning the rate of the reaction if both the temperature and concentration were increased?
The rate would increase since both factors increase the rate of the reaction.
Applications to Everyday Life:
1. Refrigerated food stays fresh for long periods. The same food stored at room temperature quickly spoils. This is because chemical reactions involved in food spoilage occur faster at room temperature than at lower refrigerator temperatures.
2. At room temperature, a bag of charcoal in contact with air does not burn. But when a starter flame touches the charcoal, atoms of the reactants( carbon and oxygen) collide with higher energy and greater frequency. These collisions are at a high enough energy to form the product ( carbon dioxide).
3. The metal next to the burners often rusts first, which is due to higher temperatures in these areas.
4. Raising the temperature of food during cooking increases reaction rates ( primarily denaturation reaction) and decreases the time required to cook the food.
Photographs: Include photos and diagrams that illustrate the how the investigation is performed.
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Video:
https://www.youtube.com/watch?v=Gn6Mo8dB1dA
Include a video of your investigation
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