Chemical reactions are all about energy changes - some release... Show more
Chemistry52 views·Updated Jun 4, 2026·2 pagesChemistry Basics: Understanding Energetics
Aliki 🩵@study_wabbit
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Energy Changes in Chemical Reactions
Every chemical reaction involves breaking old bonds (which needs energy) and forming new bonds (which releases energy). The overall energy change depends on which process requires more energy.
Exothermic reactions happen when more energy is released making new bonds than is needed to break the old ones. You'll notice the temperature rising because energy transfers from the chemicals to the surroundings. Common examples include combustion, displacement reactions, and neutralisation.
Endothermic reactions are less common but equally important. Here, more energy is absorbed breaking bonds than is released forming new ones. The temperature drops as energy is absorbed from the surroundings into the chemicals. Think photosynthesis and thermal decomposition.
Key Point: The enthalpy change (ΔH) tells you the energy change per mole - it's negative for exothermic reactions and positive for endothermic ones.
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Measuring and Calculating Energy Changes
To measure enthalpy changes experimentally, you'll use a simple calorimeter setup with a polystyrene cup, thermometer, and insulating lid. The key is minimising heat loss to get accurate results.
The essential equation is q = mcΔT, where q is heat energy, m is mass of solution, c is specific heat capacity , and ΔT is temperature change. Then calculate ΔH = q ÷ moles.
For enthalpy of combustion experiments, you burn a fuel to heat water and measure the temperature rise. Improve accuracy by using heat shields, reducing distances between burner and beaker, and covering everything to prevent heat loss.
Watch Out: Your experimental values will often be lower than theoretical ones because heat gets lost to the equipment and surroundings - this is completely normal!
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Chemistry52 views·Updated Jun 4, 2026·2 pagesChemistry Basics: Understanding Energetics
Aliki 🩵@study_wabbit
Chemical reactions are all about energy changes - some release heat whilst others absorb it from their surroundings. Understanding these energy transfers is crucial for predicting how reactions behave and calculating the exact amounts of energy involved.
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Energy Changes in Chemical Reactions
Every chemical reaction involves breaking old bonds (which needs energy) and forming new bonds (which releases energy). The overall energy change depends on which process requires more energy.
Exothermic reactions happen when more energy is released making new bonds than is needed to break the old ones. You'll notice the temperature rising because energy transfers from the chemicals to the surroundings. Common examples include combustion, displacement reactions, and neutralisation.
Endothermic reactions are less common but equally important. Here, more energy is absorbed breaking bonds than is released forming new ones. The temperature drops as energy is absorbed from the surroundings into the chemicals. Think photosynthesis and thermal decomposition.
Key Point: The enthalpy change (ΔH) tells you the energy change per mole - it's negative for exothermic reactions and positive for endothermic ones.
2
of 2Sign up to see the content. It's free!
- Access to all documents
- Improve your grades
- Join milions of students
Measuring and Calculating Energy Changes
To measure enthalpy changes experimentally, you'll use a simple calorimeter setup with a polystyrene cup, thermometer, and insulating lid. The key is minimising heat loss to get accurate results.
The essential equation is q = mcΔT, where q is heat energy, m is mass of solution, c is specific heat capacity , and ΔT is temperature change. Then calculate ΔH = q ÷ moles.
For enthalpy of combustion experiments, you burn a fuel to heat water and measure the temperature rise. Improve accuracy by using heat shields, reducing distances between burner and beaker, and covering everything to prevent heat loss.
Watch Out: Your experimental values will often be lower than theoretical ones because heat gets lost to the equipment and surroundings - this is completely normal!
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
Where can I download the Knowunity app?
You can download the app from Google Play Store and Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
Most popular content: Laws of Chemistry
1Most popular content in Chemistry
9Most popular content
9Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
4.6/5App Store
4.7/5Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan SiOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha KlichAndroid user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
AnnaiOS user