Use Hess’s Law to calculate the heat of reaction for the following reaction:

A + 3B → 3C + 2D

A + 2B → C + D H= -20 kJ

B → 2C + D H= -45 kJ

Question 10 options:

+25 kJ

-65 kJ

-25 kJ

+65 kJ

-65kJ

Explanation:

It is possible to calculate the heat of a reaction by the sum of half-reactions, thus:

(a) A + 2B → C + D   ΔH = -20 kJ

(b) B → 2C + D    ΔH = -45 kJ

The sum of (a) + (b) gives:

(a) + (b) A + 3B → 3C + 2D ΔH = -20kJ - 45kJ = -65kJ

Thus, heat of reaction is -65kJ

the answer

explanation:

the capillary tube was too close to the bottom of the beaker.

the ruler may have moved.

water got into the capillary tube.

the temperature was not allowed to equilibrate in the 2-4 minutes.

you need to take a look at the periodic system in order to sort these elements into pairs that would most likely exhibit similar chemical properties. first, you need to find elements that are found in the same group (groups are vertical in the periodic system), and then to see whether they have the same valence number. if they meet these criteria, they will have similar properties.

the first pair: ne (neon) and kr (krypton), are noble gases found in group 8

the second pair: li (lithium) and k (potassium), found in group 1

the third pair: s (sulfur) and te (tellurium), found in group 6