Calcium hydride combines with water according to the equation: #CaH_2(s) + 2H_2O(ℓ) -> 2H_2(g) + Ca(OH)_2(s)#? Beginning with with 84.0 g of #CaH_2(s)# and 36.0 g of #H_2O#, what volume of #H_2# will be produced at 273 K and a pressure of 1520 torr?

Answer 1

#22.5L#

To identify the limiting reagent, compute the moles of each of the reactants.

#M_r(H_2O)=18.0g/(mol)#
#n(H_2O)=(36.0g)/(18.0g·mol^-1)=2molH_2O#
#M_r(CaH_2)=42g/(mol)#
#n(H_2O)=(84.0g)/(42g·mol^-1)=2molCaH_2#
You have two moles of each, but in order to fully react you would need four moles of #H_2O#, since there is a #2/1# ratio. This means that #H_2O# is the limiting reagent, and for molar ratios we should use #H_2O# rather than the excess #CaH_2#.
There is a #2/2# ratio of water to hydrogen gas, which is the same as #1/1# - for every mole of water, one mole of hydrogen is produced. For two moles of water reacted in the question, two moles of hydrogen gas are produced.

You can now apply the ideal gas equation and enter all of the values that we currently know.

#PV=nRT#
where #P# is pressure, #V# is volume, #n# is the number of moles, #R# is the constant to convert between units, and #T# is the temperature.
We know that #n=2mol#, #P=1520"torr"# and #T=273K#. Since we also know the units of these values, we can find #R# from a table as #62.364(L*"Torr")/(mol*K)#.

Given that the volume is being requested, we can rewrite the ideal gas equation and enter these values to obtain

#V=(nRT)/P#
#=(2*62.364*273)/1520approx22.4L#
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Answer 2

To find the volume of H2 gas produced, first, calculate the moles of CaH2 and H2O. Then, determine the limiting reactant. Next, use stoichiometry to find the moles of H2 produced. Finally, apply the ideal gas law to calculate the volume of H2 at the given conditions.

  1. Moles of CaH2: 84.0 g / molar mass of CaH2.
  2. Moles of H2O: 36.0 g / molar mass of H2O.
  3. Determine the limiting reactant.
  4. Calculate moles of H2 produced using the limiting reactant.
  5. Apply the ideal gas law: PV = nRT, solve for V using the moles of H2, temperature (273 K), and pressure (1520 torr).
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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

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