A sample of K(s) of mass 2.720 g undergoes combustion in a constant volume calorimeter at 298.15 K. The calorimeter constant is 1849 J K−1, and the measured temperature rise in the inner water bath containing 1439 g of water is 1.60 K.

Part A

Calculate ΔU∘f for K2O.

Express your answer to three significant figures and include the appropriate units.

Part B

Calculate ΔH∘f for K2O.

Express your answer to three significant figures and include the appropriate units.

A) The ΔU° of is -361 kJ/mol.

B) The ΔH° of is -362 kJ/mol.

Explanation:

Heat released by the reaction = Heat absorbed by the calorimeter + Heat absorbed by the water

where,

q = heat released by the reaction

= heat absorbed by the calorimeter

= heat absorbed by the water

= specific heat of calorimeter =

= specific heat of water =

= mass of water = 1439 g

= change in temperature =

Now put all the given values in the above formula, we get:

m = mass of substance= 2.50 g

n = moles of substance

According to reaction , 2 moles of K gives 1 mole of

Then 0.06974 moles of K will give:

of

12,591.64 Joules of energy was released when 0.03487 mol of are formed.

So, the enthaply of formation of : ΔU°

The ΔU° of is -361 kJ/mol.

= moles of gases on RHS - moles of gasses on LHS

The ΔH° of is -362 kJ/mol.

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