Question

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

Answer 1

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.