A chemical reaction releases 2.34 kJ of heat and no work is done on the surroundings. What happens to the change in internal energy?
The change in internal energy (ΔU) is equal to the heat released during the reaction (q), since there is no work done by the system:
ΔU = q = -2.34 kJ
The negative sign indicates that the internal energy of the system has decreased by 2.34 kJ as a result of the exothermic reaction.
If 5.00 g CaCO3 reacted with 5.00 g HCl. Determine the limiting reagent?
CaCO3+2HCl → CaCl2 + CO2 + H2O
(Molar mass: Ca 40g/mol; O 16 g/mol; C 12 g/mol; Cl 35.5 g/mo; H 1g/moll)
First, we need to calculate the number of moles of each reagent:
n(CaCO3) = 5.00 g / 100.09 g/mol = 0.04996 mol
n(HCl) = 5.00 g / 36.46 g/mol = 0.137 mol
Then, we need to calculate the theoretical number of moles of HCl needed to react with all the CaCO3:
n(HCl) = 2n(CaCO3) = 0.09992 mol
Since the actual amount of HCl is greater than the theoretical amount needed, HCl is in excess and CaCO3 is the limiting reagent.
Therefore, CaCO3 will react completely with 0.09992 mol of HCl, while the remaining HCl (0.137 mol - 0.09992 mol = 0.03708 mol) will be left unreacted.