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Topic: Chemical Changes

Essential Question: How do you know when a new substance has formed?. Topic: Chemical Changes. A chemical change is when matter has changed into a new substance through a chemical reaction.

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Topic: Chemical Changes

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  1. Essential Question: How do you know when a new substance has formed? Topic: Chemical Changes

  2. A chemical change is when matter has changed into a new substance through a chemical reaction. • The animation to the right shows a chemical change. The blue and white molecule is more attracted to the red and white atoms than the green atom so they switch, forming a new substance. What is a chemical change? Animation from: http://www.ias.ac.in/initiat/sci_ed/resources/chemistry/sn2.gif

  3. A chemical change occurred when you combined baking soda and vinegar. • Vinegar makes the water more acidic. • When the molecules in baking soda mix with the acid, some of their atoms are more attracted to the acid and they break apart to form new molecules. Baking Soda Vinegar • Baking soda and vinegar are like two couples dancing. When they are separate from each other they stay with their own molecule… Why did baking soda and vinegar bubble?

  4. A chemical change occurred when you combined baking soda and vinegar. • Vinegar makes the water more acidic. • When the molecules in baking soda mix with the acid, some of their atoms are more attracted to the acid and they break apart to form new molecules. Baking Soda Vinegar • But when the two molecules mix, atoms from one molecule are more attracted to the other molecule… Why did baking soda and vinegar bubble?

  5. A chemical change occurred when you combined baking soda and vinegar. • Vinegar makes the water more acidic. • When the molecules in baking soda mix with the acid, some of their atoms are more attracted to the acid and they break apart to form new molecules. Sodium, and other stuff H2O CO2 • …So they switch dance partners and form new substances. • Notice that nothing was created or destroyed… just changed. Why did baking soda and vinegar bubble?

  6. 1. Formation of a gas • Seeing bubbles or gas after mixing substances together is evidence that a chemical change took place. What are the evidence of a chemical change?

  7. What are the evidence of a chemical change? 2. Color Change • Seeing a color change after mixing substances together is evidence that a chemical change took place. From: http://www.youtube.com/watch?v=yqUghaS5apk • A chemical color change only happens when a NEW color appears from the mixture. • Color change doesn’t always mean that a chemical change occurred, like when one substance takes over a color that was already there.

  8. 3. Temperature Change • Noticing a temperature change after mixing substances together is evidence that a chemical change took place. • The substance can get warmer or cooler, depending on whether the molecules give energy while swapping places (warmer), or need energy to swap (cooler). What are the evidence of a chemical change?

  9. 4. Formation of a Precipitate • A precipitate forms when a substance come out of solution, and form a solid. Seeing a solid substance forming after mixing substances together is evidence that a chemical change took place. What are the evidence of a chemical change?

  10. Write a 4-5 sentence summary over the topic. • Glue your Cornell Notes into the Right page of your notebook. • Complete your chose of Top Ten assignment #1, #2 or #3 on the Left page of your notebook. Finished with Notes

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