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problem 1: Hess's Law in the laboratory

Nitrous acid (HNO2) is an unstable compound when prepared by the following reaction:

HCl (g) + NaNO2 (s) → HNO2 (l) + NaCl (s).

As the product of the above reaction is unstable, the enthalpy cannot be determined directly in the laboratory. Use Hess’s law to determine the enthalpy of the above reaction using the information below.

2 NaCl (s) + H2O (l) → 2 HCl (g) + Na2O (s) Δ Ho = 506.89 kJ
NO (g) + NO2 (g) + Na2O (s) → 2 NaNO2 (s) Δ Ho = -427.17 kJ
NO (g) + NO2 (g) → N2O (g) + O2 (g) Δ Ho = -42.89 kJ
2 HNO2 (l) → N2O (g) + O2 (g) + H2O (l) Δ Ho = 33.07 kJ

Quote your answer to one decimal place.

problem 2: Heat Capacity Revision
Determine the amount of energy (heat) in joules required to raise the temperature of 9.08 g water from 25 ºC to 66.1 ºC. The heat capacity of water, that is the amount of energy required to raise the temperature of one gram of water by oneCelsius degree, is 4.184 J g−1 ºC−1. Quote the answer to 2 significant figures.

problem 3: Heat Capacity of Calorimeter

A student adds 45.1 g of water to a calorimeter and allows the temperature to stabilize in a thermostat bath at 25.00°C.

Next, s/he adds 55.8 g of 100.0°C water.

The final temperature of the entire apparatus comes to 44.2°C.

What is the effective heat capacity of the calorimeter in J/°C?

Take the specific heat capacity of water as 4.184 J g-1°C-1

Include a unit in your answer. Enter all parts of the unit in single line format. For ex, if your unit is mol L-1, present this as mol L-1. If your unit contains °C, please present this as C rather than °C.

problem 4: Enthalpy of reaction of magnesium with dilute HCl

In a different experiment, the student uses another calorimeter with a heat capacity of 133.1 J/°C. S/he fills the calorimeter with 100.0 g of 25.00°C dilute HCl solution and adds 0.510 g Mg metal (24.3 g/mol). The final temperature of the apparatus comes to 41.85°C.

What is the enthalpy change for the reaction as written?

Mg(s) + 2 HCl(aq) → MgCl2(aq) + H2(g)

Take the specific heat capacity of the dilute acid solution as being equal to that of water, and neglect the heat capacity of the magnesium metal.

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  • Category:- Chemistry
  • Reference No.:- M9606

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