Select all of the following reactions that are endothermic. ½N 2(g) + 3/2H 2(g) → NH 3(g) + 11.0 kcal/mole
H 2(g) + ½O 2(g) → H 2O(g), ΔH = -57.83 kcal/mole
½N 2(g) + O 2(g) + 8.1 kcal → NO 2(g)
½N 2(g) + ½O 2(g) → NO(g), ΔH = +21.6 kcal/mole
NH 3(g) → ½N 2(g) + 3/2H 2(g), ΔH = +11.0 kcal/mole

½N 2(g) + O 2(g) + 8.1 kcal → NO 2(g)

½N 2(g) + ½O 2(g) → NO(g), ΔH = +21.6 kcal/mole

NH 3(g) → ½N 2(g) + 3/2H 2(g), ΔH = +11.0 kcal/mole

General Formulas and Concepts:

Thermochemistry

Explanation:

An endothermic reaction would have heat or energy gained in the final stage of the reaction.

This means that our enthalpy would be positive and heat/energy would be added as a reactant.

Out of all the answer choices, we see that only these have heat/energy added in the reactant side or the enthalpy being positive:

½N 2(g) + O 2(g) + 8.1 kcal → NO 2(g)

½N 2(g) + ½O 2(g) → NO(g), ΔH = +21.6 kcal/mole

NH 3(g) → ½N 2(g) + 3/2H 2(g), ΔH = +11.0 kcal/mole

Topic: AP Chemistry

Unit: Thermochemistry

b..

is the correct one

explanation:

covalent bonds form as valence electrons are shared between two atoms. lewis structures and structural formulas are common ways of showing the covalent bonding in organic molecules. formal charge describes the changes in the number of valence electrons as an atom becomes bonded into a molecule.

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.