Question

For the reaction:

C(graphite) + O2(g) CO2(g), ?H = –393 kJ
How many grams of C(graphite) must be burned to release 275 kJ of heat?
22.3 g
0.70 g
12.0 g
17.1 g
8.40 g

Answer 1

To release 275 kJ of heat, 8.40 grams of C(graphite) must be burned, based on the given reaction enthalpy.

Step-by-step explanation:

To find out how many grams of C(graphite) must be burned to release 275 kJ of heat, we can use the given reaction enthalpy:

C(s) + O₂(g) → CO₂(g), ΔH = – 393 kJ

This indicates that – 393 kJ of heat are released when 12.0 grams of carbon (the molar mass of carbon is 12 g/mol) are burned. To release 275 kJ of heat, we need to set up a proportion:

– 393 kJ / 12.0 g = 275 kJ / x g,

solving for x gives:

x = (275 kJ * 12.0 g) / – 393 kJ ≈ 8.40 g

Therefore, 8.40 grams of C(graphite) must be burned to release 275 kJ of heat.