A2.50 g sample of powdered zinc is added to 100.0 ml of a 2.00 m aqueous solution of hydrobromic acid in a calorimeter. the total heat capacity of the calorimeter and solution is 448 j/k. the observed increase in temperature is 21.1 k at a constant pressure of one bar. calculate the standard enthalpy of reaction using these data.

The standard enthalpy of the reaction is -248.8 kJ/mole

Explanation:

Step 1: The balanced equation

Zn(s) + 2HBr(aq) → ZnBr2(aq) + H2(g)

This means for 1 mole of Zinc we need 2 moles HBr consumed, to produce 1 mole of ZnBr2 and 1 mole of H2

Step 2: Calculate number of moles of Zinc

Number of moles of Zinc = mass of Zinc / Molar mass of zinc

Number of moles of Zinc = 2.50 grams / 65.38 g/mol = 0.038 moles

Step 3:  Calculate moles of  HBr

for 1 mole of Zinc we need 2 moles HBr consumed, to produce 1 mole of ZnBr2 and 1 mole of H2

Number of moles of HBr = Molarity * volume

Number of moles HBr = 2 M * 0.1 L = 0.2 moles

Step 4: find the limiting reactant

Zinc is the limiting reactant, there will react 0.038 moles

HBr is the reactant in excess, there will remain 0.2 -2* 0.038 = 0.124 moles

Step 5: Calculate heat absorbed by calorimeter.

Heat absorption = tot. heat capacity * Temperature

Q = 448 J/K * 21.1 K

Q = 9452.8 J

Step 6: Calculate heat per mole of Zn

ΔH = 9452.8 J /0.038 moles = 248757. 9 J/mole = 248.8 kJ/mole

Since heat is given off , it's negative so -248.8 kJ/mole

c)red bank

explanation:

red bank is a borough in monmouth county, new jersey, incorporated in 1908 and located on the navesink river, the area's original transportation route to the ocean and other ports.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.