Lesson 1: Energy Changes Overview
Video Lesson
Competencies
By the end of this lesson, students will be able to:
- Define and describe endothermic and exothermic reactions.
- Explain energy changes in chemical reactions.
- Conduct simple experiments to demonstrate energy changes during chemical reactions.
- Interpret energy diagrams to understand energy transfer.
Brainstorming Questions
- Does your body sweat when you take a hot shower after an intensive physical exercise?
- Why do you burn wood, or charcoal at your home? What energy change is involved?
- The major component of dynamite is nitroglycerin, a very unstable material, mixed with diatomaceous earth. What type of energy change occurs when dynamite explodes?
Key Terms
- Endothermic Reaction
- Exothermic Reaction
- Enthalpy (ΔH)
- Calorimeter
A chemical reaction that absorbs heat from its surroundings.
A chemical reaction that releases heat to its surroundings.
A thermodynamic quantity that represents the total heat content of a system. It is the sum of the internal energy (U) of the system and the product of its pressure (P) and volume (V).
A scientific instrument used to measure the amount of heat absorbed or released during a chemical or physical process, such as a reaction or phase change.
1.1. Energy in Chemical Reactions
Energy is a fundamental part of chemical reactions, as reactants and products often have different internal energy levels. When a chemical reaction occurs, energy can be either released or absorbed. This energy change is classified into two main types:
- Exothermic reactions: These reactions release energy in the form of heat. A common example is the combustion of carbon, where energy is released as heat and light:
C(s) + O2(g) → CO2(g) + heat
Another example is dissolving sodium hydroxide in water, which heats up the solution.
- Endothermic reactions: These reactions absorb energy from their surroundings, causing a drop in temperature. For instance, the dissolution of potassium nitrate in water is an endothermic process that cools the solution.
KNO3(s) + heat → K+(aq) + NO3−(aq)
Energy Diagrams
Energy diagrams illustrate the energy levels of reactants and products during a reaction:
- In exothermic reactions, the energy of the products is lower than that of the reactants, indicating energy release.
- In endothermic reactions, the products have higher energy than the reactants, signifying energy absorption.
The Role of Enthalpy (ΔH)
The enthalpy change (ΔH) is the difference between the energy of the products and the reactants. For exothermic reactions, ΔH is negative, while for endothermic reactions, ΔH is positive.