Conservation of mass Flashcards
What is the conservation of mass?
During a chemical reaction, no atoms are destroyed and no atoms are created so same number of atoms on each side of a reaction equation
No mass is lost or gained - mass is conserved during a reaction
add up relative formula masses on each die of balanced symbol equation and you can see Mr of all reactants is equal to total of products - see page 125
In some experiments, you might observe a change of mass of an unsealed reaction vessel during a reaction.
There are usually two explanations for this
What is one explanation?
1) If mass increases its probably because one of reactants is a gas found in air and product is solid, liquid or aqueous .
Before reaction, gas is floating in air and not contained in reaction vessel so you can’t account for its mass.
When gas reacts to form part of product, it becomes contained inside the reaction vessel - so total mass of the stuff inside the reaction vessel increases. Example =Metal react with oxygen in an unsealed container, the mass of the container increases. The mass of metal oxide produced = to the total mass of metal and oxygen that reacted from the air
What is the other explanation ?
If the mass decreases, it’s probably because one of products is a gas and all the reactants are solids, liquids or aqueous .
Before reaction, all reactants are contained in reaction vessel. If the vessel isn’t enclosed, then the gas can escape from the reaction vessel as it’s formed. It’s no longer contained in reaction vessel so you can’t account for its mass - total mass of stuff inside the reaction vessel decreases. Example: Metal carbonate thermally decomposes to form metal oxide and co2, the mass of reaction vessel will decrease if it isn’t sealed but in reality the mass of metal oxide and co22 produced will equal to mass of metal carbonate that decomposed.
