Calorimetry (1 Viewer)

_Anonymous

Member
Using the equation Q = mcΔt, if Q is positive; the reaction is said to be endothermic. If Q is negative, the reaction is said to be exothermic. What confuses me is that when we perform the experiment in school, we pour an Ionic compound into a beaker filled with water and measure the final and initial temperatures.

Regardless of that, I don't understand how if Q is positive (i.e. final temp of water > initial temp of water) the reaction is said to be endothermic. Wouldn't the substance be RELEASING heat into the Water, thus making the temperature of the water warmer (by reading off thermometer) and thus Q is positive?

Likewise, if Q is negative (i.e. final temp of water < initial temp of water) the reaction is said to be exothermic? Wouldn't the substance be ABSORBING the heat from the Water making the temperature of the water be cooler, thus producing a negative Δt and hence a negative Q?

ConquerHSC

Member
Hey there,

When chemical bonds are formed, heat is generally released into the surroundings (e.g water) Reaction enthalpy (delta H) is negative for an exothermic reaction because the products have lower enthalpy than the reactants. This is because energy is released during bond formation. Since energy is released, you will measure an increase in final temperature.

When chemical bonds are broken, heat is generally absorbed from the surroundings (e.g. water). Reaction enthalpy (Delta H) is positive for an endothermic reaction because the products have higher enthalpy than the reactants. This is because energy is absorbed during the breaking of chemical bonds. Since energy is absorbed, you measured that your final temperature will be lower than your initial temperature.

<3

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_Anonymous

Member
Hey there,

When chemical bonds are formed, heat is generally released into the surroundings (e.g water) Reaction enthalpy (delta H) is negative for an exothermic reaction because the products have lower enthalpy than the reactants. This is because energy is released during bond formation. Since energy is released, you will measure an increase in final temperature.

When chemical bonds are broken, heat is generally absorbed from the surroundings (e.g. water). Reaction enthalpy (Delta H) is positive for an endothermic reaction because the products have higher enthalpy than the reactants. This is because energy is absorbed during the breaking of chemical bonds. Since energy is absorbed, you measured that your final temperature will be lower than your initial temperature.

<3
Oh I see, that clears up the confusion. Thanks so much!

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