Oquizy

Hydrogen gas reacts with chlorine gas to form hydrogen chloride according to the following equation: H₂ + Cl₂ → 2HCl. The bond energies of the relevant bonds are:
- H–H = 436 kJ/mol
- Cl–Cl = 243 kJ/mol
- H–Cl = 431 kJ/mol.
What is the overall enthalpy change?

+179 kJ/mol +272 kJ/mol –183 kJ/mol –430 kJ/mol

Why is a flame or spark needed to start an exothermic reaction?

To form stable bonds To increase pressure To lower activation energy To supply energy to break initial bonds

A student heats 50.0 g of water from 20 °C to 30 °C. Given c = 4.18 J/g°C for water.
What is the energy absorbed? What is the energy absorbed?

209 J 2090 J 4180 J 50 J

Xinyi let 25 cm³ of 1.0 mol/dm³ HCl react with 25 cm³ of 1.0 mol/dm³ NaOH. She recorded the temperature rise = 6.5 °C.
Given water density is 1.0 g/cm³, find ΔH in kJ/mol.

–13.6 –27.2 –54.4 –6.5

John mixes 30 cm³ HCl with 30 cm³ NaOH. The temperature change is 6.0 °C. What is total energy released?

1005 J 1505 J 2004 J 2510 J

Quiz: Chemistry - Chemical Energetics