A coffee cup
calorimeter contains 0.0375 mol HCl dissolved in 1.50 x 10^2 mL of water at
20.51 C. When 1.75g of solid zinc metal is placed in the calorimeter, the
temperature rises to 29.02 °C. Assume
that no heat is lost to the surroundings.
Write the balanced equation for the reaction that takes place in
the calorimeter. 1pt
Balanced reaction
Zn (s) + 2 HCl (aq) --> ZnCl2(aq) + H2
(g)
Find the limiting reactant. Show your work. 2 pts.
Number of moles of Zn = given mass of Zn / molar mass of
Zn
= 1.75
g Zn / 65.3.9 g/mol
= 0.02676 moles Zn
In equation
1 mole of Zn react with 2 mol of HCl
Hence 0.02676 moles Zn react with = 2
x 0.02676
=
0.05352 mol of HCl
But required
moles of HCl (0.05352 mol) > given moles (0.0375)
Hence HCl
is limiting reagent
Find the amount of heat lost or gained by the calorimeter. Show
your work. 2pts.
Formula of heat change, ∆T = T2 - T1 = 29.02 - 20.51 = 8.51 °
C
Specific heat capacity for
water , C = 4.184 J/g-C
Mass of
water m =
1.50
x 102 ml = 150 g (for water 1 ml = 1 g )
Use formula of enthalpy
change ∆H = m * C *∆T
Plug the values
∆H = 150 g x 4.184
J/g-C x 8.51 C
∆H = 5341 Joules
Divide by 1000 to convert in
kJ
∆H = 5.34 KJ
Temperature
is increasing so that it is a exothermic reaction
And for all
exothermic reaction ∆H is always
negative
energy lost by reaction and gained by solution. hence calorimeter gain this energy
energy lost by reaction and gained by solution. hence calorimeter gain this energy
So final answer will ∆H = - 5.34 KJ
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ReplyDeleteA coffee cup calorimeter contains
ReplyDeletedelta(q)= mcdeltaT
Deletewhen doing m is only the grams of solution or do i need to add the mass of solid zinc (1.75g)
i have a question for the mass when calculation the amount of heat lost or gained is only the grams of the hcl dissolved in water or should i add the 1.75 g of solid zinc?
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