Hi there, I need help with these two chemistry gas/pressure questions. Please sh

Question

Hi there,

I need help with these two chemistry gas/pressure questions. Please show your work. Thank you.

Q1) A 9.82 g sample of 2-ethylhexanal (formula C8H16O), is mixed with 29.39 atm of O2 in a 1.96 L combustion chamber at 333 °C. The combustion reaction to CO2 and H2O is initiated and the vessel is cooled back to 333 °C.

What is PCO2 (in atm) in the combustion chamber assuming the reaction goes to completion? Assume all water is water vapour and that the volume of the system does not change.  

Q2) an alloy of mass 40.0 g and at a temperature of 14.51 °C is placed in a calorimeter containing 47.0 g of dichlorobenzene at 88.81 °C. If the final temperature of the alloy and dichlorobenzene is 60.56 °C, calculate the specific heat (in J/g/K) of the metal. The specific heat of dichlorobenzene is 1.13 J/g/K. Express your answer to three significant figures in scientific notation.

Explanation / Answer

1.

MM(C8H16O) = 128g/mol
9.82g / 128g/mol = 0.07671mol

PV/RT = 29.39atm*1.96L / 0.082*(333+273)K = 1.1592 mol of O2
initially concentration of CO2 and H2O is zero, as combustion initiate it will increases to 0.07671 mol
=>O2 = 17.5mol
CO2 = 0.07671mol
H2O = 0.07671mol

Tot = 17.65mol

P = nRT/V = 17.65*0.082*(333+273)/1.96 = 447.5atm

2.

In these types of problems, energy (heat) is flowing from the hot material to the cold material. The energy terms are always equal to each other.

In this case, the dichlorobenzene is cooling down and the metal is warming up.

Energy = mass * heat capacity * temperature change,

Let’s convert temp in K

14.51 C = 287.21 K

88.81 C = 361.81 K

60.56 C = 333.56 K

For the dichlorobenzene, energy = 47 g * 41.13 J/g/K * (333.56K - 361.81 K) = -2825.0 J, the energy term is negative because the water is cooling off so it's giving off heat.

This energy is used to raise the temperature of the metal, you use the same equation but the sign is then positive because the metal is absorbing the energy

2825.0 J = 40.0 g * specific heat * (333.56 K - 287.21 K), specific heat = 1.52 J/gK

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