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Ksju [112]
3 years ago
14

The reaction nacl(s) → nacl(aq) is performed in a coffee cup calorimeter, using 100 ml of h2o(l) and 5.00g of nacl. if the tempe

rature of solution after mixing decreased by 2.30°c, what is the δhrxn in kj/mol? assume the heat capacities of all solutions are 4.18 j/g°c, and densities of all solutions are 1.00 g/ml. the molar mass of nacl is 58.44 g/mol
Chemistry
1 answer:
MrRissso [65]3 years ago
5 0

Since the density of water is 1 g /mL, hence there is 100 g of H2O. So total mass is:

m = 100 g + 5 g = 105 g

 

=> The heat of reaction can be calculated using the formula:

δhrxn = m C ΔT

where m is mass, C is heap capacity and ΔT is change in temperature = negative since there is a decrease

 

δhrxn = 105 g * 4.18 J/g°C * (-2.30°C)

δhrxn = -1,009.47 J

 

=> However this is still in units of J, so calculate the number of moles of NaCl.

 

moles NaCl = 5 g / (58.44 g / mol)

moles NaCl = 0.0856 mol

 

=> So the heat of reaction per mole is:

δhrxn = -1,009.47 J / 0.0856 mol

δhrxn = -11,798.69 J/mol = -11.8 kJ/mol

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How much heat is lost when 575 g of molten iron at 1825 K becomes solid at 1181 K and cools to 293 K?
meriva
Answer is: -963,8 kJ.
Q₁ = m(Fe) · C · ΔT₁.
C - specific heat capacity of liquid iron, C(Fe) = 0,82 J/g°<span>C.
</span>m(Fe) = 575 g.
ΔT₁ = 1181 - 1825 = -644°C.
Q₁ = -859306,5 J = -859,3 kJ.
Q₂ = m(Fe) · C · ΔT₂.
ΔT₂ = 293 - 1181 = -888°C.
C - specific heat capacity, C(Fe) = 0,44 J/g°C.
Q₂ = -224664 J = -224,66 kJ.
Q₃ =- heat of fusion, ΔH = 209 J/g.
Q₃ = 120175 J = 120,17 kJ.
Q = Q₁ + Q₂ + Q₃ = -963,8 kJ.

7 0
3 years ago
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A cube of plastic 1.2x10^-5 km on a side has a mass of 1.1 g. what is its density in g/cm^3
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Length of 1 side 1.2*10^-5km =1.2*10^-5*10^5 =1.2cm 

<span>volume of the cube (1.2)^3=1.728 cm^3 </span>

<span>density= mass/volume= 1.1/1.728=0.636 g/cm^3</span>
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What are blocks of time in the geological time scale called?
Katena32 [7]
B is the answer , i got you
7 0
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How do you know if the reaction is exothermic
MArishka [77]
Hey there!
Exothermic reactions release heat, causing its temperature to fall. If the reaction is lessening the temperature of the object while releasing all the heat, then you know that the reaction is indeed exothermic. Hope this helps!
5 0
3 years ago
Will mark as Brainliest.
SVETLANKA909090 [29]
<span>If I done the math correctly it is 3729J because you multiply 16.5 g  by the 2260 J/g and get 3729 J</span>
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3 years ago
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