Chemical or Physical
Which is a physical change:
- freezing water
- burning paper
- change in odor
Freezing water: change of state
2H2 + O2 --> 2H2O.
How many molecules of H do you have reacting?
4
Hot particles move faster or slower than cold particles?
Faster
What does the formation of bubbles in a reaction indicate?
A gas is being produced.
What usually happens to reaction rate when temperature increases?
It increases.
What properties will we see with a physical change? Give me 3.
- shape
- state
- size
2Ca + Cl2 --> 2CaCl
How many Ca and Cl atoms are at work in this equation?
2 of each!
Energy is released. Temperature will __________.
Decrease.
What does an unexpected color change indicate?
A chemical change occurred.
What effect does stirring have on reaction rate?
It increases the reaction rate.
What changes will we see with a chemical change? Tell me 4.
- Color change
- Change in odor
- Burning
- Precipitate forms
Is this balanced? If not, balance it!
Zn + 2HCl --> ZnCl2 + H2
Yes!
Temperatures increase when energy is ______________.
absorbed
What does a temperature increase without external heating indicate?
A chemical reaction.
Why does watering down vinegar slow the baking soda reaction?
The concentration decreases.
Substance 1 is a colorless liquid with an acidic smell. Substance 2 is a red, odorless substance. The product is a colorless, odorless solid. What kind of change occurred?
A chemical change!
Is this balanced? If not, balance it!
Fe(OH)3 --> Fe2O3 + H2O
No!
2Fe(OH)3 --> Fe2O3 + 3H2O
What are 2 factors that influence the rate of reaction? (There are 4)
Increasing concentration
Increasing temperature
Increasing surface area
Using a catalyst
What does it mean when the properties of the reaction products are completely different from the reactants?
A chemical change has taken place.
How does crushing a solid reactant affect reaction rate?
It increases surface area, which increases reaction rate.
Can you test one property to figure out if you have had a chemical change occur? Why or why not?
NO! You can't always see when a chemical change occurs so you must test multiple properties to determine if you have a different substance! At least 4-5 properties such as density, melting point, and boiling point.
If 1 molecule with 2 hydrogen atoms reacts and produces something with 6 hydrogen atoms, the equation must be wrong because this was not followed.
The law of conservation of mass/matter
In our Choose a Chemical Process Lab, which process did select to use for your instant cold pack and why?
Ammonium and water
What is it called when a solid forms after mixing two liquids?
Formation of a precipitate.
Why do reactions slow down over time?
The reactants are being used up.