Learning Objectives

• Define and compare exothermic and endothermic chemical reactions based on energy release or absorption.

• Describe how to track thermal energy transfer as it flows through a system.

• Identify and apply design criteria and constraints when creating or evaluating a solution.

• Explain how testing and modifying a design leads to the best possible solution.

Key Vocabulary

Exothermic Reaction

An exothermic reaction is a chemical process that releases energy, usually in the form of heat.

Endothermic Reaction

An endothermic reaction is a chemical process that absorbs energy from its surroundings, often feeling cold.

Thermal Energy

Thermal energy is the total energy of moving particles in an object, which we feel as heat.

System

In science, a system is a specific group of interacting parts that are being studied together.

Reactants

Reactants are the starting substances that are present at the beginning of any chemical reaction.

Products

Products are the new substances that are formed as a result of a chemical reaction.

Key Vocabulary

Design Criteria

These are the specific requirements, or goals, that a design must achieve to be successful.

Design Constraints

These are the limitations or challenges, such as time and materials, on a design project.

Combustion

Combustion is a chemical reaction that occurs between a fuel and an oxidant to produce heat.

Exothermic vs. Endothermic Reactions

Exothermic Reactions

• This type of reaction releases thermal energy, causing the surroundings to feel warmer as a result.

• Energy is transferred from the reaction to the environment, which you can often feel as heat.

• A common example of an exothermic reaction is the process of combustion, like a burning fire.

Endothermic Reactions

• This type of reaction absorbs thermal energy, causing the surroundings to feel colder as a result.

• Energy is transferred from the environment and is absorbed into the chemical reaction itself.

• A practical example is a chemical cold pack, which gets cold after being activated for use.

Exothermic Example: Combustion

• A combustion reaction is a burning process that always uses oxygen (O₂) as a reactant.

• ​Reactants, like wood and oxygen, rearrange to form new products like CO₂ and H₂O.

• This releases energy as heat and light: Wood + O₂ → CO₂ + H₂O + Energy.

Fireworks: Combustion in Action

• Fireworks are a real-world example of an exothermic reaction.

• The fuse ignites the black powder fuel, starting a planned combustion reaction.

• Combustion releases heat, light, sound, and motion to create the spectacular display.

• Carefully planned reactions produce safety and visual effects.

Defining Success: Criteria & Constraints

Criteria

• Criteria are the requirements a design must meet to be considered successful.

• They describe the necessary features or functions the solution must have.

• For example, a hand warmer must heat to 100°F in less than a minute.

Constraints

• Constraints are the limitations or challenges that restrict the design process.

• These often include the total cost of materials, time, and safety rules.

• Engineers must work within these limits to find a successful solution.

The Iterative Design Process

• First, identify and research the problem to understand its criteria and constraints.

• Brainstorm multiple ideas and create a design for the most promising solution.

• Build a model of your solution, called a prototype, and test its performance.

• Analyze test results and repeat the cycle to improve and optimize your design.

Engineering Practices in Thermal Energy Design

• Engineers ask questions to understand the problem, requirements, and limitations, like designing a hand warmer or cold pack.

• They build small prototypes to test how well the device releases or absorbs thermal energy.

• Engineers plan tests to measure temperature changes and how fast energy is transferred.

• They analyze test results to see which design works best and meets criteria.

• Engineers share their findings and suggest improvements to make the device safer and more effective.

Engineering Practices in Thermal Energy Design (Part 2)

• Engineers use math to analyze data from a thermal energy device, such as temperature changes and energy transfer.

• The core task is designing solutions that meet criteria (like target temperature and safety) within given constraints (like materials, cost, or time).

• They use evidence-based arguments to compare different designs and determine which works best.

• Engineers must clearly communicate findings and evaluate information from tests and research to improve the device.

Common Misconceptions

Summary

• Chemical reactions can be exothermic (release energy) or endothermic (absorb energy).

• Combustion is a common exothermic reaction that requires oxygen.

• The Engineering Design Process is a cycle of testing and modifying to improve solutions.

• A successful solution meets all defined criteria and stays within its constraints.