Conceptual Energy
what is energy?
ability to do work (ability to use force to move object over a distance)
A 150.0-g sample of metal is heated to a temperature of 100.0 °C and put in a calorimeter that contains 250.0 g of water. If the water’s temperature rises from 24.4 °C to 28.1 °C, what is the specific heat capacity of the metal? Ignore the calorimeter in your calculation.
0.36 J/g°C
Which substance takes less energy to raise its temperature, one with higher specific heat capacity or one with lower specific heat capacity?
lower
If heat energy is added to a substance, but the temperature does not change, what is happening?
phase change
Name one possible set of units for specific heat capacity.
J/(g degC) (energy unity divided by the product of a mass unit and a temp unit)
Which kind of reaction (endothermic or exothermic) will raise the temperature of the surroundings?
exothermic
A 115.0-g sample of glass (c = 0.840 J/g⋅°C) is dropped in a calorimeter that contains 150.0 grams of water. If the water starts out at 24.0 °C and ends up at 29.0 °C, what was the initial temperature of the glass? Ignore the calorimeter in your calculations.
61 °C
A 75.0-kg sample of lead (c = 0.160 J/g⋅°C) starts out at 16.0 °C. If it ends up at 24.1 °C, how much energy was involved in the change? Did the sample gain or lose that energy?
gained 97,000 J
How much energy is required to melt 2.21 kg of copper (Lf = 205 J/g, Lv = 4,730 J/g)?
453,000 J
Name one set of units for heat capcity.
calories/deg C (energy unit divided by temp unit)
Which substances have more energy in an exothermic reaction, the reactants or the products?
reactants
An object has a heat capacity of 11.1 J/°C. If it starts out at 25.1 °C and ends up at 45.7 °C, how much energy was involved in the change? Did the object gain or lose that energy?
gained 229 J.
When I go to McDonald's I usually get a Quarter Pounder with cheese, if the energy in the Quarter Pounder can heat 10,000 grams of water 50 degrees C, how many Calories are in a sandwich?
500
What kind of energy is in chemical bonds - kinetic or potential?
potential
A 225.0-gram sample of metal is heated to 125.0 °C and dropped into a calorimeter that has a heat capacity of 1,170 J/°C. The calorimeter contains 250.0 grams of water at an initial temperature of 24.4 °C. If the water’s temperature rises to 28.5 °C by the end of the experiment, what is the specific heat capacity of the metal?
0.42 J/g°C
. A 17.8-gram sample of an unknown metal loses 1.2 kJ of heat. The metal’s temperature lowers from 94.3 °C to 24.6 °C. What is the specific heat capacity of the metal in J/g⋅°C?
0.97 J/g°C
How much energy is required to vaporize a 115.0-g ice cube that is initially at a temperature of -11.0 °C? (cice = 2.093 J/g⋅°C, Lf = 334 J/g, Lv = 2,260 J/g.)
absorbed 349,000 J.
Give me a unity for heat
calorie, Calorie, joule
How is temperature different from heat energy?
Temperature is a measure of how quickly molecules are moving. Heat is energy that is exchanged because of a difference in temperature or a change in phase. (During a phase change heat is added to a substance but the temperature does not change)
A 275.0-gram sample of silver (c = 0.240 J/g⋅°C) is heated to 100.0 °C and dropped into a calorimeter whose heat capacity has not been measured. The calorimeter contains 300.0 grams of water at a temperature of 25.3 °C. If the final temperature of the water is 28.5 °C by the end of the experiment, what is the heat capacity of the calorimeter?
200 J/°C.
150.0 g of water in its liquid phase gains 1,600 J of heat. If it started at a temperature of 25.0 °C, what is its final temperature?
27.5 °C
Name a unity for latent heat
J/g