Two solutions, initially at 24.60°c, are mixed in a coffee cup calorimeter (ccal = 15.5 j/°c). when a 100.0 ml volume of 0.100 m agno3 solution is mixed with a 100.0 ml sample of 0.200 m nacl solution, the temperature in the calorimeter rises to 25.30°c. determine the dh°rxn for the reaction as written below. assume that the density and heat capacity of the solutions is the same as that of water. nacl(aq) + agno3(aq) → agcl(s) + nano3(aq) dh°rxn = ?

Hey there!:

moles of AgNO3 = 100 x 0.1 / 1000 = 0.01

moles of NaCl = 100 x 0.200 / 1000 = 0.02

volume of solution = 100 + 100 = 200 mL

mass of solution = 200 x 1 = 200 g

temperature rise = 25.30 - 24.60 = 0.70ºC

Therefore:

Q = m* Cp* ΔT + Cp* ΔT =

200* 4.184 * 0.70 + 15.5 * 0.70  =

Q = 596.61 J

Given the reaction:

Q = 596.61 J

NaCl(aq) + AgNO3(aq)> AgCl(s) + NaNO3(aq)

1 mole NaCl 1 mole AgNO3 1 mole AgCl

0.02 moles NaCl 0.01 moles AgNO3

So:

ΔH =  - Q / T

ΔH =  - 596.61 * 10⁻³ / 0.01

ΔH  = - 59.66 kJ

Hope that helps!

1. the question asks the most appropriate, which seems to rule out "all of the above." your choice appears to be the correct one.

2. the protocol described is good for identifying correlation, but not cause and effect. for cause/effect, you need to devise a protocol that will assign the treatment (or not) to groups that have essentially the same "demographics" with respect to all the other variables. your choice regarding control group seems appropriate. random assignment of treatment (choice d) may be appropriate also. (i think you can argue that b and d are just different descriptions of the same method.)

3. d will randomize the birds, but may not guarantee there are 10 in each group. e will do both, so seems the better choice.

comment on question 2

based on the problem statement, it seems clear that confident, attentive drivers are more likely to use daytime running lights. so, the protocol might need to be devised in such a way that the lights would be turned on or off without the driver's knowledge. (an attentive driver will figure it out.) assigning a confident, attentive driver to a group required to drive without running lights might mess with his/her confidence and attentiveness. you don't want your experiment to do that. (nor do you want the experiment to subject a driver to greater risk of accident as a consequence of driving without running lights.) experiments involving human safety are always problematic.

the answer is 1260

you spend 7 hours in school for 1 school day with 5 school days in 1 school week with 36 school weeks in a school year.

7*5*36= 1260 it's all about multiplying