Select all of the following equations that represent an exothermic reaction.

1 answer:

3 0

Exothermic reactions:

1) release heat to the surroundings

2) the change of enthalpy, ΔH, is negative: ΔH < 0

3) the temperature of the system increases

With that you can conclude about every equation given:

<span>NH3(g) + 12.0 kcal → ½N2(g) + 3/2 H2(g) : is not exothermic because heat in the side of the reactants means that heat is being used, not released.

C(graphite) → C(diamond), ΔH = - 0.45 kcal : is exothermic because ΔH is negative

C + 2S → CS2, ΔH = 27,550 cal: is not exothermic because ΔH is positive

CH4 + 2O2 → CO2 + 2H2O + 212,800 cal : is exothermic because heat appears as a product of the reaction, which means that it is released.

2H2O → 2H2 + O2, ΔH = +58 kcal : is not exothermic because ΔH is positive.</span>

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The four isomers of the compound is shown in the figure.

In an organic molecule the chiral -C center is that where four (4) different groups are present. In 3-bromo-4-fluorohexane the 3 and 4 positions are chiral centers. The possible isomers of a molecule can be obtained from the formula 2n. As here 2 chiral centers are present thus number of stereoisomers will be 2×2 = 4.

The four different isomers as shown in the figure are 3R-, 4R-; 3S-, 4S; 3R, 4S and 3S-, 4R- 3-bromo-4-fluorohexane.

In the 3-bromo-4-fluorohexane the functional groups are -Br, C₂H₅, -C₃H₆F and -H for 3-position and -F, -C₂H₅, -C₃H₆ and -H for 4-position respectively.

The priority of the -3 position will be Br > C₃H₆F > C₂H₅ > H and for -4 position F > C₃H₆Br > C₂H₅ > H. If the rotation from the higher priority group to lower is clockwise and anticlockwise then the S- and R- notation are used respectively. However if the -H atom is present at the horizontal position then the notation will be reverse.

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