The G values given in the question relate to the reactions' thermodynamics. A negative G value means that a reaction is thermodynamically spontaneous. A spontaneous reaction can occur without further energy input. This does not tell us anything about the reaction's rate (kinetics). A spontaneous reaction may be slow or it may be fast. 

A catalyst lowers the activation energy of a reaction. This could be accomplished through stabilization of the transition state by lowering its energy. A catalyst does not change the free energy difference between products and reactants, so no change in G of the reaction is observed.

This question is asking us to determine what effect a pH change would have on the reaction in which ATP is hydrolyzed into ADP. First, we have to realize that if pH were lowered, that means we are dealing with a more acidic solution. A more acidic solution, in turn, means that we have an increased concentration of . So, in essence, the question is asking what effect an increased  concentration will have on the reaction. In the reaction, we can see that  is on the product side of the reaction (on the right side). Therefore, if we drive the  concentration up, the reaction will be pushed toward the left according to Le Chatelier's principle. Furthermore, it's important to note that changing the concentration of any of the reactants or products will not have an effect on the equilibrium constant, . In fact, it is precisely because the equilibrium constant doesn't change that the reaction will shift to the left, so that the constant will remain just that, constant. Moreover, the only thing that can change an equilibrium constant is the temperature at which the reaction takes place.

The Gibbs free energy  becomes less favorable, or more positive, as enthalpy  increases and entropy  decreases.

Because  for the reaction is negative, it is spontaneous and proceeds favorably to the right. Equilibrium does not occur when the concentrations of reactants and products are equal; it occurs when the rates of forward and reverse reactions are equal. At equilibrium  thus there is no net change in the concentration of either the reactants or the products.

If two complementary single strands of DNA are put into a solution, they will spontaneously form dsDNA.  This process results in a loss of heat from the system - demonstrating that it is an enthalpically favorable process.  However, it is entropically unfavorable given the formation of a more ordered structure.

Insulin is produced by pancreatic beta cells in response to a rise in blood sugar, which occurs after eating a meal rich in carbohydrates (sugars and starches). It causes other cells of the body to take up the blood sugar (primarily glucose) and use it for energy production, and it prompts the liver to store excess glucose as glycogen. Glucagon is produced when blood sugar is too low, and it blocks glycolysis and prompts liver cells to convert stored glycogen back to glucose and release it and also produce glucose through gluconeogenesis. This is always determined by the ratio of the levels of two hormones - if there is far more insulin than glucagon, its physiological effects will dominate. There is never absolutely zero of either hormone unless the individual is diabetic to such a degree that their cells cannot produce insulin. 

A negative change in Gibbs free energy means that a reaction will take place spontaneously. By using the equation:

We can see that if both entropy and enthalpy are positive,  will only be negative when  is sufficiently high.

Reaction coupling is the pairing of one unfavorable reaction to another reaction that is favorable. The energetics of the favorable reaction drive the unfavorable one forward.

It is a common misconception that at chemical equilibrium, movement between the product and reactant sides of the equation has stopped. In reality, reactants and products are still converting back and forth to one another, however there is no longer any net movement from one side of the equation to the other. Also, Q=Keq at equilibrium.