The volume of a sample of hydrogen is 771.8 ml and it exerts 638.7 mm hg pressure at 6.5 ºc. what volume does it occupy at standard temperature and pressure? select one: a. 653 b. 2.73e4 c. 664 d. 861

627mL (May be something is wrong with the choices)

Explanation:

First step: Ideal gas Law to get the moles

P . V =  n . R . T

where P is pressure in atm (638.7 mmHg)

V is volume in L

n, the number of moles, the unknow value at this time

R the Ideal gas constant 0.082 L.atm/mol.K

T, the temperature in K (°C + 273)

760 mmHg ___ 1 atm

638.7 mmHg ___ (638.7 /760) = 0.84 atm

771,8 mL / 1000 = 0.7718 L

6.5°C + 273 = 279.5 K

0.7718 L . 0.84atm = n. 0.082 L.atm/mol.K . 279.5K

0.7718 L . 0.84atm /0.082 mol.K/L.atm . 279.5K = n

0,028 moles = n

Standard temperature and pressure are 273K and 1 atm

1 atm . Volume = 0,028 moles . 0.082 L.atm/mol.K . 273K

Volume = (0,028 moles . 0.082 L.atm/mol.K . 273K) /1atm

Volume = 0,6268 L = 627mL

answer : third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol

explanation :

let us write down the given equations

equation 1 :

equation 2 :

equation 3 :

let us use hess's law to find out which 2 equations can be added to get the third equation.

let us reverse equation 2 and multiply it by 2. the new equation that we get is,

equation 4 :

let us add equation 1 & 4

the above equation is similar to equation 3 but has different value for dhrxn.

therefore third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol