# Reaction Rates: When Surface Area Matters!

9th-12th
Group Size
2-4 students
Active Time
70 minutes
Total Time
70 minutes
Area of Science
Chemistry
Key Concepts
Reaction rate, chemical reaction, surface area, collision theory
Learning Objectives
• Understand how chemical reactions can be controlled and manipulated
• Calculate average rates of chemical reactions from experimental data
• Relate rates of chemical reactions to surface area of a reactant and frequency of collisions between reacting particles
Credits
Svenja Lohner, PhD, Science Buddies

## Overview

How does surface area affect the speed of a chemical reaction? Let your students find out in this sizzling lesson plan! In this project, they will explore this correlation by crushing Alka-Seltzer® tablets into different sized particles and measuring how long it takes for them to dissolve in water.

## NGSS Alignment

This lesson helps students prepare for these Next Generation Science Standards Performance Expectations:
• 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 lesson focuses on these aspects of NGSS Three Dimensional Learning:

 Science & Engineering Practices Disciplinary Core Ideas Crosscutting Concepts Planning and Carrying Out Investigations. Make directional hypotheses that specify what happens to a dependent variable when an independent variable is manipulated. Asking Questions and Defining Problems. Ask questions that can be investigated within the scope of the school laboratory, research facilities, or field (e.g., outdoor environment) with available resources and, when appropriate, frame a hypothesis based on a model or theory. Analyzing and Interpreting Data. Analyze data using tools, technologies, and/or models (e.g., computational, mathematical) in order to make valid and reliable scientific claims or determine an optimal design solution. Solutions. Make a quantitative and/or qualitative claim regarding the relationship between dependent and independent variables. Apply scientific ideas, principles, and/or evidence to provide an explanation of phenomena. PS1.B: Chemical Reactions. Chemical processes, their rates, and whether or not energy is stored or released can be understood in terms of the collisions of molecules and the rearrangements of atoms into new molecules, with consequent changes in the sum of all bond energies in the set of molecules that are matched by changes in kinetic energy. PS3.A: Definitions of Energy. These relationships are better understood at the microscopic scale, at which all of the different manifestations of energy can be modeled as a combination of energy associated with the motion of particles and energy associated with the configuration (relative position of the particles). In some cases the relative position energy can be thought of as stored in fields (which mediate interactions between particles). This last concept includes radiation, a phenomenon in which energy stored in fields moves across space. Cause and Effect. Changes in systems may have various causes that may not have equal effects. Scale, Proportion, and Quantity. Algebraic thinking is used to examine scientific data and predict the effect of a change in one variable on another (e.g., linear growth vs. exponential growth). Stability and Change. Change and rates of change can be quantified and modeled over very short or very long periods of time. Some system changes are irreversible.

## Materials

Materials required for the reaction activity including: a measuring cup, tape, spoon, scale, stopwatch, paper, water, and alka-seltzer tablets.

Materials for teacher preparation and demonstration:

• Measuring cylinder (250 mL) or measuring cup
• Scale
• Optional: 8 cubes of the same size (any material works)

Materials per group of 2–4 students:

• Alka-Seltzer® tablets (or other effervescent tablets) (3)
• Timer or stopwatch
• Sheet of paper
• Heavy object to crush the tablet such as a hammer or metal spoon
• 250 mL beaker or 8 oz. cup
• Tap water
• Sink

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9th-12th
Group Size
2-4 students
Active Time
70 minutes
Total Time
70 minutes
Area of Science
Chemistry
Key Concepts
Reaction rate, chemical reaction, surface area, collision theory
Credits
Svenja Lohner, PhD, Science Buddies
Learning Objectives
• Understand how chemical reactions can be controlled and manipulated
• Calculate average rates of chemical reactions from experimental data
• Relate rates of chemical reactions to surface area of a reactant and frequency of collisions between reacting particles
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