3. Which statement descobes a chemical change? 1) Alcohti evaporates
2) Table salt (NaCl) is crushed into powder
3) Water vapor forms snowflakes
4) Glucose (C6H12O6) and oxygen produce CO2 and H2O

Given the following at 25c calculate delta hf for hcn (g) at 25c. 2nh3 (g) +3o2 (g) + 2ch4 (g) > 2hcn (g) + 6h2o (g) delta h rxn= -870.8 kj. delta hf=-80.3 kj/mol for nh3 (g), -74.6 kj/mol for ch4, and -241.8 kj/mol for h2o (g)