Week 1 Flashcards
What is the principle of atom economy?
“Synthetic materials should be designed to maximise the incorporation of all (starting) materials used in the process into the final product.” Thus, atom economy aims to reduce the ‘loss’ of atoms in the manufacturing process.
E.g. retaining more of the 100 original N atoms in fertiliser when consumed (currently only 4 N atoms are consumed in a carnivorous diet).
What is a chemical equation?
“Is a statement, expressed in symbolic form that states information about a chemical reaction.”
What is the law of conservation of matter?
“Matter is neither created nor destroyed.”
Atoms are just redistributed in a chemical reaction so that the total number of atoms of each element in the reactants is the same as in the products.
What is a chemical reaction / chemical change?
“A process in which one or more new chemical species form as a result of redistribution of atoms, ions, or electrons.”
What is the law of conservation of mass?
“The total mass of substances that ready is the same as the total mass of substances that are formed.”
What does ‘chemical species’ refer to?
“Any particles that are all identical, that have characteristic chemical behaviour.”
They may be atoms, molecules or ions.
Each state of a chemical may be a unique chemical species if it behaves differently. (E.g. Cu2+ (aq), Cu2+ (s))
What is a balanced chemical equation?
“A chemical equation that satisfies two requirements;
- The total of electrical charge on the species that react is equal to the total charge on the species that forms.
- It must be consistent with the law of conservation of atoms. The number of chemical species on each side must be equal.”
What CAN a balanced chemical equation tell us?
“What the reactants are, what products are formed, and their physical states.”
“Also gives relative amounts in moles that react, and are formed, by means of the stoichiometric coefficient.” - mole ratios.
What can a balanced equation NOT tell us?
“How much of the starting materials were present, how much of the substances reacted, the natural tendency of the reaction to happen, whether heat is evolved or absorbed how fast the reaction happens, nor the mechanism of reaction.”
“1. The exact amounts of species that react, only the relative amount (ratios).
- The amounts of substances initially in a reaction mixture.
- Anything about the ‘natural tendency’ of a reaction to happen (the direction of reaction for a reaction mixture to come to chemical equilibrium).
- Whether the reaction is accompanied by the release or intake of energy, nor how much energy when the reaction occurs.
- How fast a reaction proceeds.
- Anything about the reaction mechanism (how the reaction happens at a molecular level (how the atoms rearrange themselves)).
What is a natural tendency?
“The direction that will take a reaction mixture toward the condition of chemical equilibrium, regardless of whether this reaction is fast or infinitely slow.”
(The direction the substance ‘wants’ to react, the opposite can also occur where it is HARD for a substance to react as it is not it’s natural tendency.)
E.g.
2Na(s) + Cl2(g) —> 2NaCl(s) = natural tendency
2NaCl(s) —-> 2Na(s) + Cl2(g) = NO natural tendency (will not react under ordinary pressures & temps)
What is the ‘spontaneous direction of reaction’?
“The direction of reaction that takes a reaction mixture toward the condition of chemical equilibrium.”
The reactant species in a reaction proceeding in the spontaneous direction have higher chemical potential than the products. The higher a chemical’s potential the less stable it is.
The product species in a reaction proceeding in the spontaneous direction are more stable than the reactant species.
Stability is relative; any statement of stability should use comparisons.
What is the direction of a spontaneous reaction governed by?
Whether the total ‘free energy’ of the reaction mixture increases or decreases upon reaction.
What is dynamic chemical equilibrium?
When a reaction appears to have stopped and change cannot be observed at the macroscopic level, there is evidence that the reaction in one direction is counterbalanced by the reaction that is also happening in the opposite direction, at the same rate at a molecular level.
There may still be significant quantities of reactant species as well as product species left, but their concentrations do not change.
How far a reaction goes before it reaches chemical equilibrium is different from reaction to reaction.
What does it mean if a chemical reaction ‘goes to completion’?
When the reaction proceeds until there is essentially none of one or the other (or. both) reactant species remaining.
What happens to the stability in a reaction mixture at equilibrium?
The mixture of reactants and products is more stable than either a reaction mixture containing only reactants, or a reaction mixture containing only products.
