1. A gas expands and does p-v work on the surroundings equal to 279j. At the same time it absorbs, 216j of heat from the surroundings. What
is the change in energy of the system?

Please answer if yk

The change in energy of the system : -63 J

Further explanation

Given

279 J work

216 J heat

Required

The change in energy

Solution

Laws of thermodynamics 1

ΔU=Q+W

Rules :

receives heat, Q +  releases heat, Q -  work is done by a system, W -  work is done on a system, W +  

a gas work on the surrounding : W =-279 J

a gas absorb heat from surrounding : Q = +216 J

Internal energy :

= -279+216

= -63 J

The oxidation state of sulfur, S, is +6, and the oxidation state of oxygen, O, is - 2:

S: 6+O: 2-

Explanation:

Application of rules

1. Ion SO₄²⁻

In a neutral compound, the sum of the oxidation states of all the atoms that constitute the compound is equal to zero. In ions the sum of the oxidation states of the atoms is equal to the charge of the ion.

In this case, the ion SO₄²⁻ has charge negative 2: - 2

2. Oxygen

With the exception of the peroxides, when oxygen is combined with other elements, it always has oxidation state - 2.

Hence, the total charge of the four atoms of oxygen in SO₄²⁻ is 4×(-2) = - 8.

3. Sulfur

Therefore, naming x the unknown oxidation state of S, you can set this equation:

x + ( - 8) = - 2⇒ x = - 2- ( - 8) = - 2 + 8 = + 6

Conclusion

In SO₄²⁻, the oxidation state of sulfur, S, is +6, and the oxidation state of oxygen, O, is - 2.