Chapter 6- mastering chemistry Flashcards
What is thermochemistry?
Thermochemistry is the study of the relationship between chemistry and energy
why is thermochemistry important?
It is important because energy and its uses are critical to our society. It is important to understand how much energy is required or released in a process.
what is kinetic energy? and example
Kinetic energy is energy associated with the motion of an object
examples: water at the top of niagara falls
gas molecules
raging river
what is potential energy? and example
Potential energy is energy associated with the position or composition of an object
Examples of potential energy are a curling stone sliding down the ice, a compressed spring, and molecules.
what is the SI unit of energy? list some other common units of energy
The SI unit of energy is kg m2 s−2, defined as the joule (J), named after the English scientist James Joule. Other units of energy are the kilojoule (kJ), the calorie (cal), the Calorie (Cal), and the kilowatt-hour (kWh).
a friend claims to have constructed a machine that creates electricity but requires no energy input. explain why you should be suspicious of your friends claim
According to the first law, a device that would continually produce energy with no energy input, sometimes known as a perpetual motion machine, cannot exist because the best we can do with energy is break even.
what is a state function?
State functions are the values which depend on the state of the substance like temperature, pressure or the amount or type of the substance
what is internal energy? is internal energy a state function?
The internal energy (U) of a system is the sum of the kinetic and potential energies of all of the particles that compose the system. Internal energy is a state function
if the internal energy of the products of a reaction is higher than the internal energy of the reactants, what is the sign of ΔU for the reaction? in which direction does energy flow?
If the reactants have a lower internal energy than the products, Usys is positive and energy flows into the system from the surroundings
how is the change in internal energy of a system related to heat and work?
The internal energy (U) of a system is the sum of the kinetic and potential energies of all of the particles that compose the system. The change in the internal energy of the system (U) must be the sum of the heat transferred (q) and the work done (w): U = q + w.
what is heat capacity? explain the difference between heat capacity and specific heat capacity
The heat capacity of a system is usually defined as the quantity of heat required to change its temperature by 1 °C. Heat capacity (C) is a measure of the system’s ability to hold thermal energy without undergoing a large change in temperature. The difference between heat capacity (C) and specific heat capacity (Cs) is that the specific heat capacity is the amount of heat required to raise the temperature of 1 gram of the substance by 1 °C.
If two objects, A and B, of different temperatures come into direct contact, what is the relationship between the heat lost by one object and the heat gained by the other? What is the relationship between the temperature changes of the two objects? (Assume that the two objects do not lose any heat to anything else.)
When two objects of different temperatures come in direct contact heat flows from the higher temperature object to the lower temperature object. The amount of heat lost by the warmer object is equal to the amount of heat gained by the cooler object. The warmer object’s temperature will drop and the cooler object’s temperature will rise until they reach the same temperature. The magnitude of these temperature changes depends on the mass and heat capacities of the two objects.
What is calorimetry? explain the difference between a coffee cup calorimeter and a bomb calorimeter. what is each designed to measure?
In calorimetry, the thermal energy exchanged between the reaction (defined as the system) and the surroundings is measured by observing the change in temperature of the surround- ings. A bomb calorimeter is used to measure the rU for combustion reactions. The calorime- ter includes a tight fitting, sealed container that forces the reaction to occur at constant volume. A coffee-cup calorimeter is used to measure rH for many aqueous reactions.
Which statement is true of the internal energy of a system and its surroundings during an energy exchange with a negative ?
a) The internal energy of the system increases and the internal energy of the surroundings decreases.
b) The internal energy of both the system and the surroundings increases.
c) The internal energy of both the system and the surroundings decreases.
d) The internal energy of the system decreases and the internal energy of the surroundings increases.
d) The internal energy of the system decreases and the internal energy of the surroundings increases.
We pack two identical coolers for a picnic, placing twenty-four 355 mL soft drinks and 2.5 kg of ice in each. However, the drinks that we put into cooler A were refrigerated for several hours before they were packed in the cooler, while the drinks that we put into cooler B were at room temperature. When we open the two coolers three hours later, most of the ice in cooler A is still present, while nearly all of the ice in cooler B has melted. Explain this difference.
cooler A had more ice after three hours because most of the ice in cooler B was melted in order to cool the soft drinks that started at room temperature. In cooler A the drinks were already cold and so the ice only needed to maintain this cool temperature.
