Topic 3-Quantitative chemistry Flashcards
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What is the relative formula mass of a compound?
the sum of all the relative atomic masses of the atoms in the numbers shown is the formula
What is the symbol for the unit mole?
mol
What is one mole of any substance?
an amount of that substance that contains an Avogadro number of particles
- these particles could be atoms, molecules , ions or electrons
Carbon has a relative atomic mass of 12
- What does one mole of carbon weigh?
exactly 12g
Nitrogen gas has a relative formula mass of 28 (2 * 14)
What does one mole of nitrogen gas weigh?
exactly 28g
Carbon dioxide has a relative formula mass of 44
- What does one mole of carbon dioxide weigh?
44g
Carbon has a relative atomic mass of 12?
- How many particles are in 12g of carbon?
6.02*10 to the power of 23
‘the Avogadro constant’
Nitrogen gas has a relative formula mass of 28
- How many particles are in 28g of nitrogen gas?
‘The Avogadro constant’
How is mass conserved during a reaction?
- no atoms are destroyed or created
- there are the same number of each type of atom on both sides if the equation
- so no mass is lost or gained
Why may the mass appear to change in a reaction?
When there is a gas in the reactants or products
- and the reaction takes place in an unsealed reaction vessel
Why may the mass appear to increase in a reaction?
- one of the reactants is a gas that is found in the air (e.g. oxygen)
- all the products are solids, liquids or aqueous
Explain why one of the reactants being a gas may make the mass appear to increase (during the reaction)?
- Before the reaction:
The gas is floating around in the air
It is not contained in the reaction vessel so its mass can’t be accounted for - After the reaction:
The gas reacts to form part of the product
It becomes contained in the reaction vessel
So its mass is now accounted for meaning the mass of substance in the reaction vessel increases
Give an example of when the mass of a reaction may appear to increase?
- When a metal reacts with oxygen in an unsealed container, the mass of the container increases
- the mass of metal oxide produced equals the total mass on the metal and the oxygen that reacted from the air
Why may the mass appear to decrease in a reaction?
- one of the products is a gas
- all the reactants are solid, liquid or aqueous
Explain why one of the products being a gas may make the mass appear to decrease (during the reaction)?
Before the reaction:
- all the reactants are contained in the reaction vessel and their mass is accounted for
After the reaction:
- If the vessel isn’t enclosed then the gas would have escaped as it is formed
- its mass is no long er accounted for
- the total mas of substance inside the reaction vessel decreases
Give an example of when the mass of a reaction may appear to increase?
- When a metal carbonate thermally decomposes to form a metal oxide and carbon dioxide gas
- the mass of the reaction vessel will decrease if it isn’t sealed
- however, the mass of metal oxide and the carbon dioxide produced will equal the mass of the metal carbonate that decomposed
What do the ‘big numbers’ before the chemical formulas of the reactants or products tell you?
How many moles of each substance takes part or is formed during the reaction
What does the atom economy (or atom utilistation) of a reaction tell you?
How much of the mass of the reactants is wasted when manufacturing a chemical and how much ends up as useful products
What does it mean if a reaction has 100% atom economy?
all of the atoms in the reactants have been turned into useful (desired) products
The higher the atom economy, the
‘greener’ the process
Explain the issues with a reaction having a low atom economy?
-use up resouces very quickly
- they make lots of waste that has to be disposed of (this makes these reactions unsustainable)
- usually aren’t profitable (it is expensive to but raw materials and then disposing and removing waste products responsibly)
What is he best way to get around the issue of a reaction having a low atom economy?
- find a use for the waste products rather than just throwing them away
- there is often more than one way to make the product you want, so a better reaction would have useful ‘by-products’
What reactions have the highest atom economy?
- the ones that only have one product
these have an atom economy of 100%
