Question

QUESTION 1 0.5 points Save Answer The weak acid, HX, is neutralized by sodium hydroxide as shown below: HX(aq) + NaOH(aq) - NaCN(aq) + H2000). Suppose you carried out this reaction in a coffee cup calorimeter using 50.0 mL of 0.500 M HX and 50.0 mL of 0.500 M NaOH. If the temperature of the calorimeter increases by 1.79 °C, what is the enthalpy of this neutralization reaction (in kJ/mol)? Assume the density of the solution is 1.00g/mL and that the specific heat is 4.184 J/g °C {Enter your value with the appropriate sign and value, but no units.) QUESTION 2 0.5 points Save Answer Colorless gas nitric oxide gas, NO, can react with oxygen to form the brown gas nitrogen dioxide, NO2, as shown below: 2 NO(g) + O2(g) 2 NO2(g). Suppose you wanted to carry out this reaction in the laboratory. You could filled one gas syringe with 100. mL of nitric oxide and another with 183. mL of oxygen gas. When you connected the syringes and mixed the gases, the reaction mixture changes to a brown color indicating the the reaction had occurred. If the syringes were maintained at constant temperature and pressure, what would be the expected volume of the reaction mixture after the reaction? Hint 1: it is not simply 100+183 mL. Hint 2: nitric oxide is the limiting reagent, which means the end result is a combination of the product gas and the leftover oxygen gas.

Answer 1

1. Assuming the density of solution=1.00 g/mL

Volume of solution=Volume of HX+Volume of NaOH

=50.0 mL+50.0 mL=100.0 mL

Mass of solution=Volume x Density

=100.0 mL x 1.00 g/mL

=100.0 g

As the temperature of the calorimeter increases by 1.79°C, this means heat released in the neutralisation reaction is absorbed by the calorimeter

Heat absorbed=Mass of solution x specific heat of solution x rise in temperature

=100.0 g x 4.184 J/g°C x 1.79°C=748.94 J

Number of moles of HX=Molarity x volume (L)

=0.500 M x 50.0 mL/1000 mL/L=0.025 mol

Number of moles of NaOH=Molarity x volume (L)

=0.500 M x 50.0 mL/1000 mL/L=0.025 mol

So HX and NaOH completely neutralise each other as number of moles of HX and NaOH are equal.

Enthalpy of neutralisation=-heat absorbed by the solution/number of moles of HX

=-748.94 J/0.025 mol=(-748.94 J/1000 J/kJ)/0.025 mol

=-29.96 kJ/mol

So Enthalpy of neutralisation=-29.96 (without units as asked in the question)