2: Chemistry & Biomolecules Flashcards
What is the collision theory?
Reactant molecules must collide with sufficient energy & reactants must be in the correct orientation for a reaction to occur.
What is enthalpy?
The “basic” form of energy
What is the difference between an exothermic and endothermic reaction?
Exothermic = energy is released from system into surroundings during reaction. Enthalpy change is negative
Endothermic = energy is consumed from surroundings during reaction. Enthalpy change is positive
What does a catalyst do and how?
Increases the rate of reaction, without being consumed by the reaction. Does this by lowering the activation energy
What is a feasible reaction?
A reaction is described as feasible (or spontaneous) if it is energetically favourable at a certain temp. (However the rate of reaction could still be very slow)
What are the 2 main terms which describe factors determining whether a reaction is feasible?
- Enthalpy : increase in energy
- Entropy : a measure of disorder. Disorder / randomness is thermodynamically favourable (as creating order requires external influence, time & energy)
What increases entropy of a reaction?
- Gases have more entropy than solids and liquids. Lots of small particles have more entropy than one large molecule
What is Gibbs free energy, and how is it calculated?
= The energy available in a substance to do work.
G=H-TS
enthalpy - (temp x entropy)
What are exergonic and endergonic reactions?
Exergonic = a reaction that has a negative Gibbs free energy (difference in G between products & reactants = more free energy available afterwards); so it is thermodynamically feasible.
Endergonic = a reaction that has a positive Gibbs free energy (less free energy available afterwards); so it is not thermodynamically feasible
How do unfeasible reactions occur in the body?
Must have something to provide the energy required, so is coupled with a reaction that is thermodynamically feasible. E.g. ATP synthesis from ADP is coupled with cellular respiration
How does the molecular structure of water influence its behaviour?
Water is polar (partial negative charge at O end and partial positive charge at H end), so can act as a universal solvent; and contains lone pairs of electrons that allow it to form H bonds.
Water molecules are cohesive = high surface tension.
Ice is less dense than liquid water, making it float (due to spaced out, crystalline structure when frozen)
What is the dissociation of water?
In liquid form, water molecules are always splitting apart and reforming again = dissociation. H20 splits into 2 ions ; OH- (hydroxide) ions, and H+.
The H+ released associates with another water molecule to form a hydronium/oxonium ion (H3O+)
Describe acids and bases
- An acid is a substance that donates a H+
A strong acid completely dissociates in water, e.g. Hydrochloric acid (HCl)
A weak acid partially dissociates in water (an equilibrium is formed),
e.g. Acetic acid (ethanoic acid) - A base can either : directly produce a hydroxide ion by dissociation OR pull a proton away from water to form a hydroxide ion
A strong base completely dissociates in water, e.g. potassium hydroxide
A weak base partially dissociates in water (an equilibrium is formed), e.g. ammonia.
Acids donate protons
Bases accept protons
Describe how pH buffers work (and what they do) and give examples
A buffer is a solution that can resist changes in pH after an addition of protons or hydroxide (so lessening the effect of acid).
- Consist of equal concentrations of a conjugate base acid and base
Physiological buffer systems :
e.g. Carbonic acid = converting CO2 produced by cells into HCO3 to be transported from blood into lung air space to be exhaled
Dihydrogen phosphate = involved in controlling cellular pH
What types of reactions is water involved in?
Hydrolysis: water is used to break down a compound
Condensation: a bond is formed that releases a molecule of water
