Enthalpy Change (Review)

Enthalpy change that are difficult to measure directly can often be determined using Hess's Law to construct an enthalpy change.

Which enthalpy change indicate by X in the enthalpy cycle below?

• +X enthalpy of formation of water

• -X enthalpy of formation of water

• +3X enthalpy of formation of water

• -3X enthalpy of formation of water

Farrel is challenged to match the chemical reactions with each of the enthalpy standard changes.

Please help Farrel to do his task!

• △Hat^Ө

• CH₄ + 2O₂ → CO₂ + H₂O

• △Hr^Ө

• ½ H₂(g) → H(g)

• △Hf^Ө

• 2Na + S + 2O₂ → Na₂SO₄

• △Hn^Ө

• 4Na + O₂ → 2N₂O

• △Hc^Ө

• HCl + NaOH → NaCl + H₂O

Adonis is challenged to observe the enthalpy diagram from one of the chemical reaction. Enthalpy diagram below is given to Adonis as the follow up. He wrote couple of conclusion related the the diagram one.

According your opinion which of the statement is incorrect?

• Potential energy of reactant is lower than the potential energy of product

• Reaction is endothermic

• △H = -70 kJ/mol

• Ea = 90 kJ/mol

Arya and Rio conducted the calorimeter experiment.
They mix 30.0 cm³ of 0,0250 mol dm^-3 potassium hydroxide solution with 30.0 cm³ of 0,0250 mol dm^-3 of nitric acid. The temperature rose by 0.5 ^o C. Assume no heat was lost to the surroundings.
The final mixture had a specific heat capacity of 4.2 J cm^-3 K^-1 .

Please help Arya and Rio to calculate the molar enthalpy (enthalpy change) for the reaction

Propanol has the formula C₃H₈O.
Fachry and Rossi assigned to calculate the enthalpy change for the formation of propanol.
Here are the data of enthalpy combustion several molecules:
△Hc^Ө hydrogen = -286 Kj mol^-1

△Hc^Ө carbon = -249 Kj mol^-1

△Hc^Ө propanol = -303.0 Kj mol^-1

a) Draw the cycle of this reaction!
b) What in the △Hf^Ө from this reaction?

An experiment was carried out by Kevin and Rafa to determine the approximate value for the molar enthalpy of neutralization.
75 cm³ of 3.00 mol dm^-3 hydrochloric acid was placed in a polystyrene beaker of negligible heat capacity. Its temperature was recorded, and then 75 cm³ of 3.00 mol dm^-3 potassium hydroxide at the same temperature was quickly added, and the solution was stirred.
The temperature rose by 14 ^o C. The resulting solution may be considered to have a specific heat capacity of 4.2 J g^-1 K^-1. Which calculation below is correct for help Kevin and Rafa to calculate molar heat (enthalpy change)

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The complete combustion of ethyne, C₂H₂, is shown in the equation below.

C₂H₂ + 5/2 O₂ → 2CO₂ + H₂O

Using the average bond enthalpies given in the table, what is the enthalpy change of combustion of ethyne?

Firaz want to make compound R into compound T through chemical reaction. He choose indirect way throughout produce compound S as intermediate product.
Here are the following steps were involved.
R → S : △H is positive

S → T : △H is negative

Which reaction profile fits to these data?

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