When vinegar and baking soda are combined, a chemical reaction occurs and there is a change in enthalpy. An energy graph of this reaction is provided in to the right. What type of reaction and energy
change occurred?
a. Exothermic, +AH
b. Exothermic, -AH
c. Endothermic, +AH
d. Endothermic, -AH

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.

consider the reaction below.

 no rx

at 500 k, the reaction is at equilibrium with the following concentrations.

[pci5]= 0.0095 m

[pci3] = 0.020

[ci2] = 0.020 m

what is the equilibrium constant for the given reaction?

0.042

0.42

2.4

24

they are all solids.

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.