<span>Pre-1982 definition of STP: 37 g/mol
Post-1982 definition of STP: 38 g/mol
This problem is somewhat ambiguous because the definition of STP changed in 1982. Prior to 1982, the definition was 273.15 K at a pressure of 1 atmosphere (101325 Pascals). Since 1982, the definition is 273.15 K at a pressure of exactly 100000 Pascals). Because of those 2 different definitions, the volume of 1 mole of gas is either 22.414 Liters (pre 1982 definition), or 22.71098 liters (post 1982 definition). And finally, there's entirely too many text books out there that still use the 35 year obsolete definition. So let's solve this problem using both definitions and you need to pick the correct answer for the text book you're using.
First, determine how many moles of gas you have. Just simply divide the volume you have by the molar volume.
Pre-1982: 2.1 / 22.414 = 0.093691443 moles
Post-1982: 2.1 / 22.71098 = 0.092466287 moles
Now determine the molar mass. Simply divide the mass by the moles. So
Pre-1982: 3.5 g / 0.093691443 moles = 37.35666667 g/mol
Post-1982: 3.5 g / 0.092466287 moles = 37.85163333 g/mol
Finally, round to 2 significant figures. So
Pre-1982: 37 g/mol
Post-1982: 38 g/mol</span>
Answer:
mass P4 = 35.998 g
Explanation:
∴ STP: P = 1 atm; T = 298 K
∴ V O2= 35.5 L
⇒ nO2 = P.V / R.T
∴ R = 0.082 atm.L/K.mol
⇒ nO2 = ((1 atm)×(35.5L))/((0.082 atm.L/K.mol)(298K))
⇒ nO2 = 1.453 mol O2
⇒ mol P4 = (1.453 molO2)×(mol P4/ 5molO2) = 0.2906 mol P4
∴ Mw P4 = 123.895 g/mol
⇒ mass P4 = (0.2906 mol P4)×(123.895 g/mol) = 35.998 g P4
Answer: option <span>C. the total energy inside the calorimeter will decrease.
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Justification:
The answer is a direct application of the first law of thermodynamic (the law of conservation of energy).
By telling that the t<span>he calorimeter is sealed so that there is no heat exchanged between the contents of the container and the surrounding air, the first law of thermodynamics implies that the total energy inside the calorimeter will not change.
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<span>That statement, without adding any more is enough justification.
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Regarding, the other statements, you can show they are true:
<span>A.
the thermometer will show an increase in temperature.
</span><span>
</span><span>
</span><span>Since the reaction is exothermic, the heat released will increase the temperature inside the sealed calorimeter,which, of course, is shown by the termometer.
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</span><span>
</span><span>
</span><span>B. The potential
energy of the products will be lower than that of the reactants.
</span><span>
</span><span>
</span><span>In any exothermic reaction, the potential energy of the products is lower than that of the reactants, because the heat released is lost by the reactants when they react and transform into the products.
</span><span>
</span><span>
</span><span>D. The water
increases in temperature as the reaction gives off heat</span>.
Sure. The heat cannot leave the sealed calorimeter, but the water inside the calorimeter will absorb that heat: the molecules of water will gain kinetic energy and so its temperature will be increase.
I will use this conversion:
1m = 1000 mm => 1 = 1m / 1000mm
1 m = 100 cm=> 1 = 1m / 100cm
1m = 10 dm=> 1 = 1m / 10 dm
So,
B) 3.8 * 10^7 cm^3 = 3.8 * 10^7 cm^3 * [1m / 100cm]^3 = 38 m^3
C) 3.8 * 10^5 dm^3 * [1m / 10 dm]^3 = 380 m^3
D) 3.8 * 10^8 mm^3 * [1m / 1000 mm]^3 = 0.38 m^3
Now you can compare the four volumes and conclude which is the largest.
Answer: option C) 3.8 * 10^5 dm^3
