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

What is a chemical change? 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. Animation from:

Why did baking soda and vinegar bubble? 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 and vinegar are like two couples dancing. When they are separate from each other they stay with their own molecule… Baking Soda Vinegar

Why did baking soda and vinegar bubble? 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? 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 CO 2 …So they switch dance partners and form new substances. Notice that nothing was created or destroyed… just changed. H2OH2O

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

2. Color Change ◦ Seeing a color change after mixing substances together is evidence that a chemical change took place. ◦ 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. From: What are the evidence of a chemical change?

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? 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.

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