chemistry help?

Question

1. Which one of the following statements refers most directly to enthalpy?

A.In an endothermic reaction, the sign of delta H is negative
B.Potential energy decreases in an exothermic reaction
C.Molecules in a gas spin or tumble end over end
D.Molecules in a heated metal vibrate more rapidly



2. Regarding oxidation numbers in redox reaction , which statement is true?

A.The algebraic sum of oxidation number in a molecule or compound is zero
B.Loss of an electron results in a decrease in an oxidation number
C.Oxidation numbers in a redox reaction tend to shift from left to right
D.In a redox reaction, oxidation numbers generally remain the same

Answer 1

In thermodynamics, the quantity enthalpy, symbolized by H, also called heat content, is the sum of the internal energy of a thermodynamic system plus the energy associated with work done by the system on the atmosphere, which is the product of the pressure times the volume. 1A

The term redox comes from the two concepts of reduction and oxidation. It can be explained in simple terms:

Oxidation describes the loss of an electron by a molecule, atom or ion
Reduction describes the gain of an electron by a molecule, atom or ion However, these descriptions (though sufficient for many purposes) are not truly correct. Oxidation and reduction properly refer to a change in oxidation number — the actual transfer of electrons may never occur. Thus, oxidation is better defined as an increase in oxidation number, and reduction as a decrease in oxidation number. In practice, the transfer of electrons will always cause a change in oxidation number, but there are many reactions which are classed as "redox", though no electrons are transferred (such as those involving covalent bonds).