Physical And Chemical Changes Flashcards
What is a chemical change
Produces new substances and takes place on a molecular level.
Eg. Combustion
What are signs of chemical change?
Solid (precipitate) is formed Change in colour Significant change in temp Disappearance of a solid (not dissolving) Odour Gas is evolved
What is a physical change?
Physical changes are concerned with energy and states of matter.
Does not produce a new substance.
Eg. Melting, freezing, condensation, etc
Eg. Crushing a can, melting an ice cube
What are the signs of physical change?
- change in state(liquid, solid, gas)
- Appearance(grinding rock into dust)
- dissolving a solid in a liquid
- separating mixtures
How do u tell chem and physical changes apart?
- Chem changes make new subs
- There might be clues that a chem reaction took place (light, heat)
- The starting and ending materials of a physical change are the same, even though appearance has changed
What does a chemical reaction occur?
When a chemical reaction causes bonds between atoms to break or form
What are the five types of chemical reactions that cause chemical change to occur
1) composition
2) decomposition
3) single replacement
4) double replacement
5) combustion
What is composition
Two things come together to form something new
A + B = AB
Eg. 2H2 + 02 ➡️ 2H2O
What is Decomposition?
1 thing breaks apart to form 2 or more things
AB = A + B
Eg. 2H2O = 2H2 + O2
What is a single replacement reaction
One atom replaces another
A + BC = AC + B
Or
A + BC = AB + C
Eg. Mg + 2HCl ➡️ H2 + MgCl2
What is a double replacement reaction
Two chemicals switch place
AX + BY = AY + BX
Eg. 2KI + Pb(NO3)2 ➡️ Pbl2 + 2KN3
What is combustion
A substance combines with oxygen and releases energy
Eg. C3H8 (propane) + 5O2 ➡️ 3CO2 + 4H2O
What is released during a chemical reaction
Heat
Light
What are the two types of chemical reactions
Exothermic and endothermic
