Question

Compound Δ Hrxn (kJ/mol) NH4NO3 + 25.7 KCl + 17.2 NaOH -44.5 KOH -57.6

You are given 6.7 grams of an unknown salt. You dissolve it in 54.1 mL of water. As the salt dissolves, the temperature of the solution changes from an initial temperature of 26.9°C to a final temperature of 53.9°C. Based on the chart of ΔH values and the temperature change, you can determine which salt you have. What is the temperature change? Δ T = o C Tries 0/99

This is the ΔT component of the expression: qsurr = C x mass x ΔT where qsurr is the heat lost or gained by the contents of the calorimeter due to the chemical reaction. What is the mass that is changing temperature in this experiment? mass =_______ g

Assume that the heat capacity, C, of the solution is the same as that of water, C = 4.184 J/g oC. Solve for qsurr. qsurr = J Tries 0/99 What is the value of qsys? qsys = ____J

The change in enthalpy, ΔH, of this reaction is equal to qsys, since it was carried out under conditions of constant external pressure. Based on the sign of ΔH (or qsys) the dissolution of the unknown salt is . ________

When 6.7 g of salt are dissolved in 54.1 mL of water, 6880.4 J of heat are given off by the system. How much heat would be given off if only 1.00 g of salt had been dissolved in the water? qsys =_______ J/g

In the table, the ΔH values are given in kJ/mol. Convert your last answer to kJ to give kJ/g. Finally, multiply the kJ/g by the molar masses (g/mol) of possible salts, to get kJ/mol. The reaction of your unknown salt with water was exothermic. So, you will only need to look at salts with negative ΔH values. formula of unknown = ________

Answer 1

m = 6.7 g of Salt X

V = 54.1 mL of water

dT = 53.9-26.9 = 27 °C

a)

the dT = 27°C

b)

Qsurr = C*mass*dT ...

mass required --> 6.7 + 54.1 = 60.8 g of total mass

c)

Qsurr = C*mass*dT = 4.184*60.8 * 27 = 6868.4544 J

qsys = -qsurr = -6868.4544 J

d)

this must be exothermic, i.e. it gives off energy

e)

m = 6.7 g of salt dissolve in 54.1 mL of water...6868.4544 heat are given off..

if m = 1 g is dissolved then

ratio of masses = 1/6.7 =0.14925373

then

Q = 0.14925373*6868.4544 = 1025.142 J