# hilde

Most popular questions and responses by hilde
1. ## chemistry

liquid heptane C7H16 is completely combusted to produce CO2 and H2O: C7H16 + 11O2 --> 7CO2 + 8H2O the heat combustion for one mole of C7H16 is -4.85*10^-3 CO2 heat of comb. = -393.5 H2O h of c= -285.8 a) calc. the vale of heat of cumbustion for C7H16 in

2. ## trig

if cot(- theta) = 7.89, find tan(theta- pi/2)

3. ## chemistry

in an experiment a sample of hydrocarbon was analyzed. The sample contained6 g of carbon and 1.344 g Hydrogen. a) whats the empirical formula? the density of hydrocarbon at 25 C and 1.09 atm is 1.96 g/L b.) whats the molar mass of the hydrocarbon? c) whats

4. ## chemistry

Fe2O3 + 3CO --> 2Fe + 3CO2 a 16.2 L sample of CO at 1.5 atm and 200 C is combind with 15.39 g Fe2O3. how many moles of CO are available for the reaction? what is the limiting reacta? How many moles of Fe are formed?

5. ## trig

sin²u + tan²u + cos²u/ sec u simplify

6. ## chemistry

how do u calcualte the percent of hydrogen and carbon if given their mass in grams?

7. ## trig

how do you find all the solutions when cos x = .75

8. ## trig 26

simplify to a constant or trig func. 1. sec ²u-tan ²u/cos ²v+sin ²v change expression to only sines and cosines. then to a basic trig function. 2. sin(theta) - tan(theta)*cos(theta)+ cos(pi/2 - theta) 3. (sec y - tan y)(sec y + tan y)/ sec y combine

9. ## trig

simplify to a constant or basic trig function.. 1+tan(x)/1+cot(x)