Question

Hydrogen cyanide is used in the manufacture of clear plastics such as lucite and plexiglas. it is prepared from ammonia and natural gas (ch4). 2nh3(g) + 3o2(g) + 2ch4(g) → 2hcn(g) + 6h2o(g) the reaction evolves 939 kj of heat per 2 mol hcn formed. is the reaction endothermic or exothermic?

Answer 1

Answer: The given reaction is exothermic in nature.

Step-by-step explanation:

Sign convention for
`\Delta H` :

For endothermic reaction, the enthalpy change is positive and that for exothermic reaction it is negative.

For the given chemical equation:

`2NH_3(g)+3O_2(g)+2CH_4(g)\rightarrow 2HCN(g)+6H_2O(g)`

Sign convention of heat:

When heat is absorbed, the sign of heat is taken to be positive and when heat is released, the sign of heat is taken to be negative.

To calculate the enthalpy change of the reaction, we use the equation:

`\Delta H_(rxn)=(q)/(n)`

where,

q = amount of heat released = -939 kJ

n = number of moles of HCN = 2 moles

`\Delta H_(rxn)` = enthalpy change of the reaction

Putting values in above equation, we get:

`\Delta H_(rxn)=(-939kJ)/(2mol)=-469.5kJ/mol`

Hence, the given reaction is exothermic in nature.

Answer 2

Here we have to judge the reaction between methane and ammonia in presence of oxygen to produce hydrogen cyanide is exothermic or endothermic in nature.

The reaction between methane and ammonia in presence of oxygen heat is evolved from the system thus it is an exothermic reaction.

We know the reaction in which heat escapes from the system to the surroundings are termed as exothermic. On the other hand the chemical reaction in which heat is absorbed by the system from surroundings is called endothermic reaction.

The reaction can be shown as- 2CH₄ + 2NH₃ (g) + 3O₂ (g) = 2HCN (g) + 6H₂O (g).

In this reaction to generate 2 moles of HCN 939 kJ energy is released thus it is an exothermic reaction.