What happens to two objects of two different temperatures come in contact?
Heat flows from the object with the higher temperature to the object with the lower temperature. EX: holding a cold soft-drink makes your hand cold
Define potential energy in terms of chemistry?
energy that is stored in a substance because of its chemical composition
What factors determine heat capacity?
the chemical composition of the substance and its mass
Why do you think it is important to define the system and its surroundings?
thermochemistry measures heat flow across the boundary between the system and its surroundings
Describe the sign convention that is used in thermochemical calculations
A negative sign is given to heat flow from the system TO the surroundings. A positive sign is given to heat flow to the system FROM the surroundings.
Two substances in a glass beaker chemically react, and the beaker becomes too hot to touch: EXO or ENDO?
EXOthermic
Two substances in a glass beaker chemically react, and the beaker becomes too hot to touch: the two substances are defined as systems, then what constitutes the surroundings
The immediate surroundings are the glass beaker and the air. if one or more substances is in water, than the water is also considered part of the surroundings
ENDO OR EXO: condensing steam
exothermic
ENDO OR EXO: evaporating alcohol
endothermic
ENDO OR EXO: burning alcohol
exothermic
ENDO OR EXO: baking a potato
endothermic
What name is given to a heat change at a constant temperature?
enthalpy
What is a calorimeter?
An instrument used to measure heat changes in physical or chemical processes
What are sources of error in experiments using foam cups as calorimeters?
-the foam cup will absorb some heat
-some heat will be lost to the air
-the reactants are not completely mixed
What information is given in thermochemical equations?
Amount of heat released or absorbed in a chemical change at a constant pressure (Delta H)
Explain why ice melts at 0 degrees C without an increase of temperature, even though heat flows from the surroundings to the system?
Heat is being used to melt the ice
What is the standard heat of formation of a free element in its standard state?
zero
Consider the statement "the more negative the value of (delta Hf0), the more stable the compound" T or F?
True because since the stability implies lower energy. The greater the release of heat, the more stable is the compound relative to its elements (all of which have deltaHf0)
Equal masses of two substances absorb the same amount of heat. The temperature of substance A increases twice as much as the temperature of substance B. Which substance is higher in heat?
Substance B; For equal masses, the substance with the greater heat capacity undergoes the smaller temperature change.
What is the standard heat of formation of a compound?
The standard heat of formation (deltaH0) of a compound is the change in enthalpy that accompanies the formation of one mole of a compound from its elements with all substances in their standard states at 25 degrees C
Explain why fusion is an endothermic process but freezing is an exothermic process
When a solid reaches its melting point, additional heat must be absorbed to convert it to a liquid. Therefore, fusion of a solid is endothermic. This heat of fusion is released when a liquid freezes, so freezing is exothermic.