A fundamental law stating that in any chemical reaction, the total mass of all reactants exactly equals the total mass of all products, because atoms.
Matter can't vanish or appear from nothing. What goes in equals what comes out.
Showing a random 20 of 50 problems.
Example 1
medium
28 g of nitrogen reacts with 6 g of hydrogen to make ammonia. What mass of ammonia forms (sealed)?
Example 2
medium
Why must a balanced equation obey conservation of mass?
Example 3
easy
Does the number of moles always stay the same in a reaction?
Example 4
hard
A sealed bag has 25 g of reactants. After a reaction it has the same mass but feels warm. Use conservation to identify what is and is not changing.
Example 5
medium
4 g H2 reacts with 32 g O2 to form water. What mass of water forms?
Example 6
hard
A student measures 200 g of reactants in a beaker and 188 g of solid product, with the beaker uncovered. Is this consistent with conservation of mass?
Example 7
medium
Why does the count of atoms of each element have to match on both sides of a balanced equation?
Example 8
medium
In 2H2+O2→2H2O, 4 g H2 reacts with 32 g O2. Show mass is conserved if 36 g water forms.
Example 9
medium
23 g Na reacts with 35.5 g Cl2 to form NaCl. Wait — Cl2 is in excess; only 17.75 g reacts. What mass of NaCl forms?
Example 10
easy
Who is credited with establishing the law of conservation of mass?
Example 11
medium
Why does steel wool gain mass when heated in air?
Example 12
medium
Iron wool is heated in open air and gains mass. Reconcile this with conservation of mass.
Example 13
hard
2Al+3Cl2→2AlCl3. If 5.4 g Al (M = 27) reacts completely with Cl2 to form 26.7 g AlCl3, what mass of Cl2 was used?
Example 14
easy
20 g of magnesium burns in air to form 33 g of magnesium oxide. What mass of oxygen reacted?
Example 15
easy
If 12 g of magnesium reacts with oxygen to form 20 g of magnesium oxide in a closed container, how many grams of oxygen reacted?
Example 16
challenge
Hydrogen (2 g) and oxygen (16 g) react. Only 18 g of water forms and some oxygen remains. Use conservation to find the leftover oxygen mass.
Example 17
medium
If 50 g of Pb(NO3)2 (in solution) reacts with 30 g of KI (in solution) and 35 g of PbI2 precipitate forms, what is the mass of the solution (KNO3) left over?
Example 18
easy
A reaction in an open flask appears to gain mass. What is the likely cause?
Example 19
hard
A photographer claims a reaction 'made matter disappear' because the products weigh less than the reactants. What flaw is in this claim?
Example 20
easy
10 g of A reacts completely with 15 g of B in a sealed flask. What is the total product mass?