Physical Changes
Chemical Reactions
Exothermic and Endothermic Reactions
Law of Conservation of Mass
Miscellaneous
100
Definition of physical change
A change that changes how matter looks, tastes, smells, etc., but does not change the composition of matter.
100
What are four signs that a chemical change is happening?
Fizzing/bubbling, Heat, Precipitate forms, light, sound, new odor
100
When the system loses thermal energy and the surrounding gains that thermal energy
Exothermic reaction
100
The law of conservation of mass states that
Matter cannot be created nor destroyed, only transformed
100
A substance that is made of at least 2 atoms
Molecule
200
These are the forces between molecules that determine the state of matter of a substance
Intermolecular forces
200
What are the two parts of a chemical equation?
Reactants and Products
200
Define endothermic. What happens to the system?
Endothermic means that the system is gaining thermal energy. The system becomes warmer.
200
A system that is in contact with its environment or surroundings
Open system
200
What is the difference between molecules and compounds?
Molecules are substances made of at least two atoms.
Compounds are substances made of at least two different atoms.
300
Explain why making lemonade is a physical change
Lemonade is a mixture of water, lemons, and sugar. The flavor changes but there is still water, lemons, and sugar.
300
What is a balanced equation?
An equation that shows that the number of atoms in the reactants is the same as the number of atoms in the products. It shows the law of conservation mass.
300
The reaction between calcium chloride and water feels hot to the touch. This is an....
Exothermic reaction
300
A system that does not lose mass when a gas is produced is called a
closed system
300
Is CaSO4 a molecule or compound?
CaSO4 is both because it has a total of 6 atoms (molecule) but it is also made of 3 different types of atoms, Calcium, Sulfur, and Oxygen (compound)
400
Is it possible to melt and freeze water at the same temperature? Explain.
Liquid water freezes at 0 degrees Celsius. Frozen water (ice) melts at 0 degrees Celsius. So yes, water freezes and melts at the same temperature.
400
What are the signs that a firework is a chemical change? (HINT: there are at least 5)
Heat, new color appears, new odor, light, precipitate forms
400
Explain an example of an endothermic reaction
Multiple answers
400
How is matter conserved in the following image?
The number of atoms is the same in the reactants and products:
2 H 2
1 Cl 1
1 Na 1
1 O 1
400
How many of each element are present in: 5CaSO4
5 Calcium
5 Sulfur
20 Oxygen
500
What happens to thermal energy during a phase change? What happens to temperature during a phase change? Why?
Thermal energy can increase or decrease during a phase change but temperature remains constant because all the energy is being used to break the intermolecular forces, instead of being used to raise or drop the temperature.
500
Does this equation follow the law of conservation of mass. Explain.
3C6H12O6 + O2 -> 6CO2 + 18H2O
No, the equation does not follow the law of conservation of mass because:
18 C 6
36 H 36
20 O 30
500
In terms of endothermic and exothermic reactions, what is the difference between roasting a marshmallow and burning a marshmallow?
Roasting - the marshmallow (the system) gains heat from fire to get roasted so it is becoming warmer.
Burning - the marshmallow (the system) now on fire is releasing heat to it surroundings so it's losing heat.
500
What are two pieces of evidence that mass is conserved? Explain your answer
#1 The number of grams is conserved. Started at 184.34 grams and ended at 184.34 grams.
#2 The number of atoms is conserved. Reactants: 1 Ca, 2 Cl, 2 Na, 1 S, 4 O. Products: 1 Ca, 2 Cl, 2 Na, 1 S, 4 O.
500
How many of each type of atom are there in 3Mg3(PO4)2
Mg: 9
P: 6
O: 24