What is the role of an electrophile and the role of a nucleophile?
An electrophile is a molecule that is attracted to electrons. That is, an electrophile is usually positively charged or is neutrally charged with empty orbitals that can be filled by surrounding electrons via interactions through bonding. An electrophile will ACCEPT an electron pair from a nucleophile. In contrast, a nucleophile is a molecule that DONATES electrons to an electrophile in order to form a bond. A nucleophile is usually a molecule that is negatively charged with a free pair of electrons, or a pi bond available to donate electrons. The more electrons a nucleophile has, the more reactive it will be with surrounding molecules.
An exothermic reaction with a negative change in enthalpy (H) and a positive change in entropy will be thermodynamically favorable or unfavorable? Why?
For a reaction to be thermodynamically favourable, the Gibbs free energy (G), defined as a measure of spontaneity, should be negative. The equation used to determine if a reaction is favorable is Change in G= change in H - (T*change in S). If the change in enthalpy (H), or the amount of internal energy in a system, is negative, that indicates an exothermic reaction, which is a process that releases heat into the surroundings. An exothermic process is favorable, because the reactants are at a higher energy than the products, which causes a release of heat and thus, more stable products. Furthermore, if change in entropy (S), a measure of disorder, is positive, this indicates the system is moving towards a more favorable disordered state. The entropy of any system will always spontaneously gravitate towards a system of "maximum entropy" or maximum disorder, making it the more favored result. When plugged into the equation, a negative H and a positive S will make the Gibbs Free Energy a negative number. This indicates the reaction is thermodynamically favorable and will spontaneously occur.
Describe the key differences between prokaryotic cells and eukaryotic cells.
Prokaryotes are single-celled organisms with no membrane-bound organelles, no nucleus, and DNA in the form of a singular, circular, "naked" chromosome, which contains essential heredity information (genes), stored in the cytoplasm. Prokaryotes also house non-essential genes in structures known as plasmids. They are usually very small in size, and most prokaryotes use either binary fission or budding to reproduce (asexual reproduction). Prokaryotes do not contain mitochondria, and have smaller ribosomes than eukaryotes. Prokaryotes consist of archea and bacteria. Eukaryotes are multi-cellular organisms with membrane-bound organelles, and DNA in the form of multiple, linear chromosomes contained by associated proteins in the nucleus. DNA in eukaryotes is not naked, and is wrapped around proteins known as histones. Eukaryotes do not contain plasmids.Eukaryotes are usually large in size and use mitosis and meiosis for reproduction (sexual reproduction). Eukaryotes are fungi, protists, animals and plants.