Atom economy, percentage yield and gas calculations .3

what is atom economy

The atom economy of a reaction is a measure of the amount of starting materials that end up as useful products.

what is atom economy important for

It is important for sustainable development and for economic reasons to use reactions with high atom economy.

atom economy =

what is the highest possible value of atom economy

• 100%, when all the reactant atoms end up in the desired product.

• If the atom economy is 50%, for example, then half the reactant atoms end up in the desired product or products.

what is the theoretical yield

The theoretical yield is the maximum possible mass of a product that can be made in a chemical reaction.

how can theoretical yield be calculated

It can be calculated from:

• the balanced equation,

• the mass and relative formula mass of the limiting reactant, and

• the relative formula mass of the product

why is it not always possible to obtain the calculated amount of a given product

Reasons why the mass of product made is less than the maximum theoretical mass include:

• the reaction not going to completion, because it is reversible

• some of the product may be lost when it is separated from the reaction mixture by filtering, for example

• some of the reactants may react in ways different to the expected reaction

percentage yield =

how can the percentage yield vary

• 100% (no product has been lost)

• 0% (no product has been made).

what is a reaction pathway

A reaction pathway describes the sequence of reactions needed to produce a desired product.

what does the pathway chosen for a product depends on

• percentage yield

• atom economy

• rate of reaction

• equilibrium position

• usefulness of by-products

why is the manufacture of ethanol useful and what does the manufacture of ethanol has

• The manufacture of ethanol, used as a fuel,

• provides a useful example for choosing reaction pathways

which two ways in ethanol manufactured in

• Fermentation of plant sugars (C₆H₁₂O₆(aq) → 2C₂H₅OH(aq) + 2CO₂(g)

• Hydration of ethene, obtained from crude oil, using steam (C₂H₄(g) + H₂O(g) → C₂H₅OH(l)

word equation for Fermentation of plant sugars:

glucose → ethanol + carbon dioxide

which manufacture of ethanol is more effective

• Fermentation has a lower percentage yield and rate of reaction (15% - low) than the hydration of ethene (95% - high).

• The hydration of ethene has an atom economy of 100%, showing that all the atoms in the reactants form the desired product.

• As it also has a higher rate of reaction, the hydration of ethene appears to be the better way to make ethanol.

what type of reaction is the hydration of ethene

reversible reaction

where does the equilibrium position lie in the hydration of ethene

The equilibrium position lies to the left, so only about 5% of the ethene supplied is converted to ethanol

how is the overall yield of the hydration of ethene achieved

The overall yield of 95% is achieved by recirculating unreacted ethene through the reactor.

what is carbon-dioxide a by-product of

Carbon dioxide is a by-product of the fermentation of plant sugars

who can carbon-dioxide be sold to and how does it affect its atom economy

• It may be sold to fizzy drinks manufacturers to provide the bubbles in lemonade and cola.

• This makes it a desirable product as well, so the atom economy can be increased to 100%.

what does Avogadro's law states about temperature and pressure

Avogadro's law states that when the temperature and pressure stay the same:

• equal volumes of different gases contain an equal number of molecules

• this means that equal amounts in moles of gases occupy the same volume under the same conditions of temperature and pressure

At a given temperature and pressure what does one mole of gas occupy

the same volume:

what is the molar volume

the molar volume is the volume occupied by one mole of any gas, at room temperature and pressure (same temp + pressure and isnt affected by Mr or Ar of the gas)

amount in mol =

what is the molar volume equal to

molar volume is equal to 24 dm³ (24,000 cm³)