7. methane, ch, burns in oxygen gas to form water and carbon dioxide. wequation for this reaction? a. ch4+ o h2o co2b. ch4+ 40 2h20+ co2c. ch4 o2 h2o co2d. ch4+ 202 2h20 co2
8. how many atoms are present in 3 moles of chromium? c. 1.80 x 1024 atomsa. 6.02 x 1023 atomsb. 1.80 x 1023 atomsd. 52.00 atoms
9. how many grams of co2 are in 2.1 mol of the compound? a. 21.0 gc. 66.0 gb. 44.0 gd. 92.4 g

7) the answer is D.  You need to know that oxygen gas is O₂ which means that A and B can't be right.  Then you need to see which one is balanced and since D is and C is not, the correct answer has to be D.

8)  You need to know that 1 mole of anything contains 6.02×10²³ particles.  therefore you multiply 6.02×10²³ by 3 to get 1.806×10²⁴ atoms.

9) You need to multiply the number of moles of carbon dioxide by the molar mass of carbon dioxide (44g/mol).  2.1mol×44g/mol=92.4g.  Therefore the answer is 92.4g of CO₂.

I hope this helps.  Let me know if anything is unclear.

Spontaneity tell us the direction of the reaction, but not how fast it goes. gibbs free energy brings together enthalpy, entropy and temperature in one easy formula. g = h - ts. and, finally the sign of delta g is always negative for a spontaneous reaction.