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Thermochemical Equations

#### Q. You have an unknown that is a mixture of NaCl and Na3PO4 solids. You add 10.0 grams of the unknown solid to 190.0 grams of 2.000 M HCl solution with aninitial temperature of 18.92o C in a coffee cup calorimeter. The following reaction occurs: Na3PO4(s) + 3 HCl(aq)  3 NaCl(aq) + H3PO4(aq) ∆H = -499 kJ After the reaction is complete, you find the temperature in the cup to be 37.13o C. Note: addition of the NaCl solid to the HCl solution would have no heat released or absorbed; any temperature change is due solely to the reaction with Na3PO4 solid (the limiting reagent in the reaction above). What percent of the solid mixture is Na3PO4? You may make the following assumptions. The coffee cup acts as an isolated system. The resulting solution in the cup has a specific heat of 4.18 J/go C. The density of the resulting solution is 1.04 g/mL. Mol mass: Na3PO4 = 163.91g/mol, NaCl = 58.43g/mol, HCl = 36.46g/mol, H3PO4 = 97.99 g/mol

Solved • Apr 30, 2020

Thermochemical Equations

#### Q. Liquid water can be split into hydrogen gas and oxygen gas (∆H = 285.8 kJ/mol) by applying energy through an electric current. In this experiment, 13.31 kJ of energy are applied to 12.3 grams of water in a sealed reaction vessel whose volume is 4.56 L and whose temperature is 311.15 K. Note: At 311.15 K, the vapor pressure of water is 0.0654 atm. Determine the theoretical yield in moles of hydrogen gas & moles of oxygen gas. Was limiting reactant water or energy?

Solved • Apr 1, 2020

Thermochemical Equations

#### Q. The thermochemical equation below shows the decomposition of the mineral magnesite: MgCO3(s) => MgO(s) + CO2(g) ΔHrxn = 117.3 kJ What is ΔH when 5.35 mol of CO2 reacts with excess MgO? A. 314 kJ B. -628 kJ C. 628 kJ D. -314 kJ E. none of these is within 5% of the correct value

Solved • Mar 30, 2020

Thermochemical Equations

#### Q. When one mole of methane (CH4) is burned at constant pressure, 890 KJ of energy is released as heat. Calculate the ΔH for a process in which a 5.8 g sample of methane is burned at constant pressure.

Solved • Mar 30, 2020

Thermochemical Equations

#### Q. In a certain experiment, 0.7000 mol of hydrogen gas reacted with 0.7000 mol of solid iodine at a constant 1 atm pressure, producing 1.4000 mol of solid hydrogen iodide and absorbing 36.9 kJ of heat in the process. Write the thermochemical equation

Solved • Mar 14, 2020

Thermochemical Equations

#### Q. Calculate the change in enthalpy (Delta H rxn) per mole of reagent

Solved • Feb 8, 2020

Thermochemical Equations

#### Q. How much energy is required to vaporize 158 g of butane (C4H10) at its boiling point, if its Hvap is 24.3 kJ/mol? ( Group of answer choices 66.1 kJ 89.4 kJ 15.1 kJ 38.4 kJ 11.2 kJ

Solved • Jan 16, 2020