📚

All Subjects

 > 

🧪 

AP Chem

 > 

🧪

Unit 4

4.4 Physical vs. Chemical Changes

2 min readaugust 22, 2020

Dalia Savy

Hope Arnett


What Are Chemical Equations?

Chemical equations show the products that the combination of reactants yield, but the equation doesn’t show how the reactants form those products. What we don’t see are the underlying chemical and physical changes that allow molecules to rearrange to change properties or create new substances.

Chemical Changes

Generally, chemical changes involve intramolecular (literally meaning “inside molecule”) bonds. This includes breaking and/or forming bonds between elements. Let’s look at a chemical reaction using Lewis Dot Diagrams to visualize it.
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-NdJlpeJH6yhR.png?alt=media&token=014adacc-f56f-4d2a-97f7-6d4f34fb5044
The synthesis reaction above shows an interaction between magnesium and oxygen. The bonds that are broken are red, and the bonds formed are green. Here, we can see that the oxygen’s covalent bonds had to break, and then new ionic bonds formed between the magnesium and oxygen.

Physical Changes

Physical changes are usually intermolecular changes (literally meaning “between molecules”), such as phase changes. Some examples are freezing water🧊 and cutting paper✂️📄.
The ice’s molecules maintain the same atomic structure (H2O), but more hydrogen bonds between each water molecule are formed. Conversely, the paper’s molecules keep the same atomic structure, but the interaction between the paper molecules are broken.
However, some reactions can go either way. For example, the reaction between salt and water involves breaking the bonds between ions, but it also creates ion-dipole interactions between the water and ions.

Review Activity

Name whether each scenario describes a chemical or physical change.
  1. Burning a match🔥
  2. Iron rusting over time🚲
  3. Mixing two powders🥣

Answers

  1. Burning a match is a chemical change
  2. Iron rusting is a chemical change
  3. Mixing two powders is a physical change

Resources:

Was this guide helpful?

💪🏽 Are you ready for the Chem exam?
Take this quiz for a progress check on what you’ve learned this year and get a personalized study plan to grab that 5!
START QUIZ
Hours Logo
Studying with Hours = the ultimate focus mode
Start a free study session
FREE AP chem Survival Pack + Cram Chart PDF
Sign up now for instant access to 2 amazing downloads to help you get a 5
Browse Study Guides By Unit
📆
Big Reviews: Finals & Exam Prep
✏️
Blogs
✍️
Free Response Questions
🧐
Multiple Choice Questions
⚛️
Unit 1: Atomic Structure and Properties
🤓
Unit 2: Molecular and Ionic Compound Structures and Properties
🌀
Unit 3: Intermolecular Forces and Properties
👟
Unit 5: Kinetics
🔥
Unit 6: Thermodynamics
⚖️
Unit 7: Equilibrium
🍊
Unit 8: Acids and Bases
Join us on Discord
Thousands of students are studying with us for the AP Chemistry exam.
join now
📱 Stressed or struggling and need to talk to someone?
Talk to a trained counselor for free. It's 100% anonymous.
Text FIVEABLE to 741741 to get started.
© 2021 Fiveable, Inc.