Chemical vs. Physical Changes: Let’s Get it Straight!

Breathing, cooking, exercising, and more: we are surrounded by changes every day! But how do we keep straight which are physical and which are chemical?


Physical Changes

Physical changes involve chemicals getting rearranged in a new way, but without getting destroyed or irreversibly combined. The molecular structure of the original substance(s) is the the same after the change, which means it is still the same substance. A common example is of water freezing; the liquid water becomes a solid, but it is still water. Ripping paper is another example because while it may be in pieces, it’s still paper. Signs of a physical change include:

  • Expected color change
  • Change in size or shape
  • Change in state of matter
  • Reversible
  • No new substance formed!

Chemical Changes

Chemical changes, or reactions, involve chemicals getting rearranged in irreversible ways. We bring in the term “reaction” when dealing with chemical changes because the chemicals involved actually react with one another to form a new substance (that’s why we call the parts in a chemical reaction the reactants). The ways chemicals can react are many: two substances can combine to create a totally new one (Direct Combination), a substance can permanently break apart, separating into different substances (Decomposition), or maybe a substance combusts as it reacts to oxygen (Combustion) (see more types of reactions here). Whatever the reaction, it’s important to recognize that one or more new substances are formed! Burning wood is a common example of a chemical reaction because as the wood reacts with oxygen after it has been ignited, it creates smoke and ashes. Signs of a chemical reaction include:

  • Unexpected color change
  • Change in temperature as energy is released or absorbed
  • Gas created
  • Irreversible
  • New substance formed!

Confusing Cases

In many cases, it may seem a simple task to distinguish between the two, but it gets more complex when we’re dealing with changes that seem irreversible when they’re not. For example, we may look at a glass of Kool-Aid and think to ourselves, “I made Kool-Aid. It was water and a packet, but now it’s dissolved together to make new drink, so it’s a new substance.” However, if you think back to the list of signs of a physical change, you’ll realize that not only was there an expected color change (the water didn’t turn purple when you added red Kool-Aid!), but that it is reversible–the water could evaporate in the form of gas, leaving red Kool-Aid residue behind! The water is still water, and the Kool-Aid is still Kool-Aid, and since no new substances were formed, it is a physical change!

Another example of confusion is in cooking eggs–after all, isn’t it still an egg before and after tossing it in pan? However, on a molecular level, the egg has changed completely as the proteins have bonded in new ways, making it a new substance. Additionally, because of the change, it is not possible for the egg to ever become raw again, and since a new substance was formed, it is a chemical change!

For some practice using the different lists of signs for each type of change, and to view several other examples in action, check out this Prezi below!

Photo credit: Faris Algosaibi

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Teacher Resources: Ever Heard of Reddit?

Where can you find a community of all different types of teachers who can post all kinds of resources? Ever heard of Reddit? Science, Math, English, College, Adult Ed, Art, and an almost unlimited supply of teachers can be found in this Internet community, and we’ve got a few suggestions of our own…


Reddit, directly from Wikipedia’s definition, “is a social news and entertainment website where registered users submit content in the form of links or text posts.” What does this mean for teachers? It means you now have a one-stop hub for all teaching resources you could need, not to mention worldwide feedback! Another great use for the resources on Reddit is to involve your students. There are a number of educational pages that students could use to reach out to others. See our lists below!

Don’t have an account? One of the best features about Reddit is that it takes just seconds to register an account. In the age of sharing personal information, it’s relieving to see a website ask for only what you want your username to be and what you want your password to be. Registering with an email is optional.

Don’t want to register? Fine! You can browse the site all you want, and unless you want to comment, nothing will be restricted if you simply want to “lurk.”

Now that you’ve joined the community, it’s important to understand that Reddit is divided into subreddits, which are communities of people that fulfill a particular niche. So you’re a teacher, hmm? Allow us to suggest a few subreddits to get you started:

  • /r/education: “The goal of r/Education is to provide a community in which educational stakeholders can participate in meaningful, reflective, and thought-provoking discourse about educational policy, research, technology, and politics.”
  • /r/AskAcademia: “This subreddit is for discussing academic life, and for asking questions directed towards people involved in academia, (both science and humanities).”
  • /r/highereducation: “A place to discuss and share articles related to higher education.”
  • /r/matheducation: “Anything math related that is useful for education, teachers, or students, with emphasis on usefulness for teachers, such as good internet resources, or ideas for how to teach a concept.”
  • /r/ScienceTeachers: “A place for science educators to collaborate on and contribute tips, ideas, labs, and curricula. We seek to encourage the sharing of interesting studies, experiments, videos and articles that will interest students of all ages and promote science and critical thinking in their lives.”
  • /r/teachingresources: “A place to share all your most amazing and useful resources. If we use this well, it could become a very efficient and effective way to enrich many classrooms with everyone else’s resources.”

And more:

And tons more–literally anything you could think of!

Now, get out there and contribute to the education of the masses!

*Obligatory NSFW warning, warning*: Reddit can sometimes have less-than-savory content. Most of the time, this is marked by NSFW, which stands for “Not Safe For Work.” That means you shouldn’t open that link or comments while at work, or you could violate the rules your employer likely has in place regarding Internet usage. You might also see NSFL, which stands for “Not Safe For Life,” meaning gore. If you still want to experience Reddit without these tags, take a look at the Reddit Enhancement Suite. It’s a completely free, open source browser extension that allows you filter out NSFW tags.

 

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Featured Image: Kyle Garrity