How does the equilibrium change to counter the removal of A in this reaction? A + B ⇌ AB The equilibrium shifts left. Simultaneously, there's an increase in the reverse reaction.

The increase in the reverse reaction

Explanation:

Based on the LeCh's principle, a change in the concentration of a species in the equilibrium will shift the concentrations of the other species in order to counteract the effect of this change.

For example, for the reaction:

A + B ⇌ AB

Remove A in this reaction will produce the increase in the reverse reaction in order to increase the concentration of A.

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.  

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.