Prelab (10 points) 1. Write a balanced enthalpy of formation equation for liquid
ID: 1036271 • Letter: P
Question
Prelab (10 points) 1. Write a balanced enthalpy of formation equation for liquid water starting from the elemental diatomic gases hydrogen and oxygen. Use section 9.7 on page 400 of your text to help you (2 pts.). 2. Use the following the steps (and sample problem 9.6) to calculate AH. (in kJ/mol Mg) from calorimetry if magnesium reacts with HC1 (7 pts. total). Mg (s)+2 HCI (a?) MgCl(a?)+ H (g) a. Calculate the moles of magnesium reacted if 5.00 g magnesium (MM 24.305 g/mol) reacts completely with HCl (1 pt.) b. Calculate the heat of reaction (q in J) if Mg reacts with enough HCl to make a 500.0 g solution (418 Jg C) and raises the temperature from 20.00°C to 30.13°C using the equation (2 pts.). c. Calculate the AH.,( in J) using the following equation (be sure to include the sign as + or-) (1 pt.). d. Calculate the ? Hrxn (in kJ/mol Mg) by dividing the heat calculated in part b by the number of moles of magnesium in part a and converting to kJ (2 pts.).Explanation / Answer
1.H2(g)+1/2O2(g) ----------->H2O(l) is tne reaction
2. moles of Mg= mass/atomic weight= 5/24=0.21 moles
the reaction is Mg+2HCl ---------->MgCl2+ H2
mass of the solution = 500gm, specific heat= 4.184 J/gm.deg.c, since there is temperature rise, the reaction is exothermic, So heat of reaction = 500*4.184*(30.13-20) joules=21192 joules
enthalpy change = -21192 joules
this is the heat released when 0.21 moles of Mg is burnth
enthalpy change/mole= -21192/0.21 =-100914 J/mole= -100.914 Kj/mole
since there is rise in temperature, the reaction is exothermic.
when the reaction is reversed, the reaction becomes endothermic with enthalpy change= 100.914 Kj/mole