Post on 07-Apr-2020
transcript
UNIT 2.5
The definitions of mass and matter are
inter-related
Matter- anything that has MASS and takes
up space
Mass- a measure of how much MATTER
is in an object
Do we destroy mass or
matter when we lose
weight?
• No we convert it into a
different form (fat is just
stored energy)
How do we release that
extra mass?
• Most of it is converted
into thermal and kinetic
energy to maintain and
move our bodies
Law of Conservation of Mass – during a chemical
reaction, mass is not created or destroyed
All of the atoms that are present at the beginning
of the reaction (reactants), are present at the end
of the reaction (products).
When a chemical reaction occurs, mass is never
gained or lost, it is just transferred into other
forms of the original atoms used.
massreactants= massproducts
Law of Conservation of Matter
• Law of Conservation of Matter – during a
chemical reaction, matter is not created or
destroyed
• All of the atoms that are present at the beginning
of the reaction (reactants), are present at the end
of the reaction (products).
• The mass of the matter does not change even if
the substance changes to a new phase. Ex.
Liquid water changing to gaseous water.
Saved
Keep
What goes in must come out
Reactants equal products
Changes
remains
massreactants= massproducts
“Yields”
means
equals
The reactants are Fe and S; the product is FeS
Fe weighs 14 g and S weighs 8 g.
By the conservation of mass/matter, the product, FeS, will weigh 14 g + 8g = 22 g
Consider the following reaction. Mg+ HCl MgCl2 + H2
1) What are the reactants for the reaction?
2)What are the products for the reaction
Mg and HCl
MgCl2 and H2
Mg + HCl MgCl2+ H2
10 g of Mg reacts with 14 g of HCl.
After the reaction, we have yielded 8 g of MgCl2. By the law of conservation of mass/matter, how many grams of H2 had to be formed?
Mg + HCl MgCl2+ H2
10 g + 14 g = 8g + ?
24 g = 8 g + ___ g
What number plus 8 will equal 24 g for the products side to equal the reactants side in terms of grams?
8 g + 16 g = 24 g
So H2 is 16 g
Another way to say mass is conserved is to
say that the mass of the reactants equals the
mass of the prodcuts
50 grams of sodium reacts with chlorine to form 126 grams of salt. How many grams of chlorine reacted?
Na + Cl2 NaCl 50 g + ?? = 126 g
We know the reactants have to equal the products. If
the products weigh 126 g, then the reactants must weigh 126 g.
So far, we know we have 50 g of the 126 g.
So 126 g – 50 g = 76 g of Cl2
Open System - matter can enter from or
escape to the surroundings • This is when you can have sources of matter coming
from different places
Closed System – matter is not allowed to
enter or leave
First, a tree is part of an
open system: sky, air,
and ground
When a tree is born, it
grows from changing
CO2 into sugars to add
mass. The CO2 comes
from the air.
When a tree dies, the
elements and molecules
that made up the tree do
not disappear.
The tree’s nutrients go back
into the ground and are
recycled.
There is a conservation of
mass (and matter).