Question

Part A

When 10.00 g of phosphorus is burned in O2(g) to form P4O10(s), enough heat is generated to raise the temperature of 2960 g of water from 18.0 ∘C to 38.0 ∘C.

Calculate the heat of formation of P4O10(s) under these conditions.

ΔHf =		kJ/mol

SubmitMy AnswersGive Up

Part B

Instant cold packs that are used to ice athletic injuries on the field contain ammonium nitrate and water separated by a thin plastic divider. When the divider is broken, the ammonium nitrate dissolves according to the following endothermic reaction:

NH4NO3(s)→NH4+(aq)+NO3−(aq)

To measure the enthalpy change for this reaction, 1.25 g of NH4NO3 is dissolved in enough water to make 25.0 mL of solution. The initial temperature is 25.8∘C and the final temperature (after the solid dissolves) is 21.9∘C.

Calculate the change in enthalpy for the reaction. (Use 1.0 g/mL as the density of the solution and 4.18 J/(g⋅∘C) as the specific heat capacity.)

Express the enthalpy change in kilojoules per mole to two significant figures.

ΔHrxn =		kJ/mol

SubmitMy AnswersGive Up

Part C

What is the mass of the silver block?

Express your answer with the appropriate units.

mAg =

SubmitMy AnswersGive Up

Part D

A silver block, initially at 68.1 ∘C, is submerged into 100.0 g of water at 24.6 ∘C in an insulated container. The final temperature of the mixture upon reaching thermal equilibrium is 26.6 ∘C.

What is the mass of the silver block?

Express your answer with the appropriate units.

mAg =

SubmitMy AnswersGive Up

Part E

LP gas burns according to this exothermic reaction:

C3H8(g)+5O2(g)→3CO2(g)+4H2O(g)ΔH∘rxn=−2044kJ

What mass of LP gas is necessary to heat 1.6 L of water from room temperature (25.0 ∘C) to boiling (100.0 ∘C)? Assume that during heating, 16 % of the heat emitted by the LP gas combustion goes to heat the water. The rest is lost as heat to the surroundings.

Express your answer using two significant figures.

m =		g

SubmitMy AnswersGive Up

Part F

A 2.51 g lead weight, initially at 10.6 ∘C, is submerged in 7.86 g of water at 52.4 ∘C in an insulated container.

What is the final temperature of both the weight and the water at thermal equilibrium?

Express the temperature in Celsius to three significant figures.

T =		∘C

SubmitMy AnswersGive Up

(Both G and H)

Ethanol can be made from the fermentation of crops and is used as a fuel additive to gasoline.

Part G

Write a balanced equation for the combustion of ethanol (assume the water as a product of reaction to be gaseous).

Express your answer as a chemical equation. Identify all of the phases in your answer.

SubmitMy AnswersGive Up

Part H

Calculate ΔH∘rxn.

Express your answer using four significant figures.

ΔH∘rxn =		kJ

SubmitMy AnswersGive Up

Answer 1

part A

    P4(s) + 5O2(g) -----> P4O10(s)

no of mol of P4 = 10/124 = 0.0806 mol

heat released(q) = m*s*DT

          = 2960*4.184*(38-18)

          = 247692.8

          = 247.693 kj

DH0f = - q/n = - 247.693/0.0806

      = -3073.11 kj/mol

part B

         NH4NO3(s)→NH4+(aq)+NO3−(aq)

heat absorbed(q) = m*s*DT

                 = 25*4.184*(25.8-21.9)

                 = 0.408 kj

no of mol of NH4NO3 = W/MWT = 1.25/80 = 0.0156 mol

DH0rxn = +q/n

         = +0.408/0.0156

         = +26.154 Kj/mol

part C

   heat lost by silver block = heat gained by water

    mass of silver*s*DT = mass of water*s*DT

     m*0.233*(68.1-26.6) = 100*4.184*(26.6-24.6)

   m =   mass of silver = 86.54 g