Answer:
-3.19x10³ J
Explanation:
Since the surroundings absorbed 3.19 × 10³ J (or 3190 J) of heat, the system, or the dissolution reaction, must have lost the same amount of heat. The heat for the system, then, is -3.19 × 10³ J (or -3190 J). We know this is true because of the first law of thermodynamics, "heat is a form of energy, and thermodynamic processes are therefore subject to the principle of conservation of energy".
Salt will be less soluble in water if the "temperature is decreased". The kinetic energy brought about by temperature increases as the temperature increases. Because of these increase in kinetic energy, solvent molecules (water molecules) tend to break apart effectively the solute molecules (salt molecules).
This is a combustion reaction, which always has the hydrocarbon and oxygen as reactants and then carbon dioxide and water (which is steam in this case) as products.
C8H18 + O2 —> CO2 + H2O
Balance your carbons first. You want to get 8 carbons on both sides.
C8H18 + O2 —> 8CO2 + H2O
Now balance your hydrogens. You want 18 hydrogens on both sides.
C8H18 + O2 —> 8CO2 + 9H2O
Now balance your oxygens. You have 2 on the left and 25 on the right. The O2 reactant needs a coefficient of 12.5 to balance this.
C8H18 + 12.5O2 —> 8CO2 + 9H2O
However, you can’t have decimals for coefficients in a reaction. So, multiply everything by 2.
2C8H18 + 25O2 —> 16CO2 + 18H2O
Now, use your mole ratio of 18 mol H2O for every 2 mol C8H18 to solve.
5.74 mol C8H18 • (18 mol H2O / 2 mol C8H18) = 51.7 mol H2O (steam)