Which statement is true if the mc001-1.jpghrxn of a reaction is positive? the reaction is endothermic. the reaction is exothermic. there is more reactant than product. there is more product than reactant.

The enthalpy change of a reaction is given as the difference in enthalpies of the products and reactants i.e.

ΔHrxn = ∑ΔH⁰f (products) - ∑ΔH⁰f(reactants)

If ΔH°f(products) > ΔH°f(reactants) then the value of the enthalpy change for the reaction ΔHrxn is positive.

Reactions which show a positive value of ΔHrxn proceed with the absorption of heat and are called as endothermic reactions.

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.