Energy
What is potential energy?
Potential energy is stored energy (e.g. compressed spring, dynamite, rock on cliff edge).
What is temperature?
Temperature is average kinetic energy (how fast atoms and molecules are vibrating, sliding, or bouncing).
How do particles in gases move?
Particles in gases move rapidly, randomly, and in straight lines until they collide with the walls of their container.
Why is the ideal gas law (PV = nRT) sometimes called the combined gas law?
It relates several properties that are described in other laws (ex: volume and pressure from Boyle's Law).
What does q stand for in the heat transfer equation? (q = mc𝚫T)
"q" represents energy in joules.
What is kinetic energy?
Kinetic energy is the energy of an object in motion (e.g. a bowling ball about to strike some pins).
What is heat?
Heat is energy transferred due to a temperature difference (hot object warms cool object and vice versa).
How do particles in solids move?
Atoms in solids vibrate in place rather than sliding past each other or ricocheting off the walls of their container.
What units for temperature are used in the ideal gas law? (PV = nRT)
Temperature must be in Kelvin.
How many joules of heat are needed to raise the temperature of 10.0 g of aluminum from 22°C to 55°C, if the specific heat of aluminum is 0.90 J/g°C?
297 J
What is energy?
Energy is the ability to do work (work is moving an object by applying a force).
Which substances tend to have low specific heats?
Metals tend to have low specific heats.
How do particles in liquids move?
Particles in liquids slide past each other due to moderate attractive forces.
A cylinder of helium is pressurized to 80 atm. Its temperature in Kelvin in 200 K (-73°C). It would explode if the pressure exceeds 160 atm. At what temperature would the cylinder explode?
The pressure must double, and the volume is constant, so the temperature must double. This means the cylinder must reach 400 K (127°C or 260°F).
What does n stand for in the ideal gas law? (PV = nRT)
"n" represents the number of moles (NOT GRAMS) of gas.
A piece of magnesium is dropped into concentrated hydrochloric acids. The starting temperature of the mixture is 23°C. After the metal is completely dissolved, the temperature has risen to 47°C. Is this exothermic or endothermic?
This is exothermic. The system is the two reactants (metal and acid) and heat is exiting (the water rises in temperature).
Why does a temperature difference cause heat to transfer between two objects?
The fast particle collide with the slow particles and speed them up. These collisions cause the fast particles to lose speed.
What do plateaus mean on a heat vs. temperature graph?
Plateaus mean a phase change (i.e. ice melting and becoming water at 0°C).
The volume of a gas is reduced by half. If the initial pressure was 13 atm, what will the new pressure be?
Volume and pressure are inversely proportional. If the volume is halved, the pressure will double?
Calculate the specific heat capacity of a piece of wood if 1500.0 g of the wood absorbs 67,500 joules of heat, and its temperature changes from 32°C to 57°C.
1.8 J/g°C
Is sublimation an example of endothermic or exothermic change?
Sublimation is an endothermic change. For a solid to turn into a gas, it must absorb energy.
How can the specific heat of a metal sample be determined from dropping it into a water bath and measuring the temperature change? (Hint: which law applies?)
The heat released by the metal is exactly equal to the heat absorbed by the water (conservation of energy). This can be used to determine the specific heat of metal (heat known, mass known, and change in temperature known).
Why does temperature remain constant during phase transitions?
Additional energy added to the system works to overcome attractive forces (changing movement pattern) rather than speeding up the particles (temperature).
Why does an increase in temperature result in an increase in pressure? (Use kinetic molecular theory to explain)
Higher temperature means faster particles. The faster a particle collides with the walls of the container, the more force it exerts. Pressure is force divided by energy.
How many moles of gas does it take to occupy 120 liters at a pressure of 2.3 atmospheres and a temperature of 340 K?
9.89 moles