Thermodynamics

Temperature and thermal equilibrium Temperature is the measure of the internal energy of an object. Internal energy: the energy of a substance due to the random motions of its component particles and equal to the total energy of those particles (kinetic energy)

Thermal equilibrium: the state in which two bodies in physical contact with each other have identical temperatures. Thermal expansion: the phenomenon where the volume of a substance increases as the its temperature increases. –This is the basis for the working of a thermometer

Measuring Temperature The most common device to measure temperature is a thermometer and it use the concept of thermal expansion. Temperature scales –Fahrenheit is the most common in the U.S. –Celsius is used in the metric system –Kelvin is the absolute temperature scale.

Heat: the energy transferred between objects because of a difference in their temperatures. Energy is transferred as heat from the higher-energy particles to lower-energy particles The net energy transferred is zero when thermal equilibrium is reached

At thermal equilibrium, the net energy exchanged between two objects equals zero.

Conservation of Energy A vessel contains water. Paddles that are propelled by falling masses turn in the water. This agitation warms the and increases its internal energy. The temperature of the water is then measured, giving an indication of the water’s internal energy increase

If a total mass of 11.5 kg falls 1.3 m and all of the mechanical energy is converted to internal energy, by how much will the internal energy of the water increase? (Assume no energy is transferred to the surroundings

A worker drives a.075 kg spike into a rail tie with a 3.25 kg sledgehammer. The hammer hits the spike with a speed of 65.0 m/s. If one –third of the hammer’s kinetic energy is converted to internal energy of the hammer and spike, how much does the total internal energy increase?

Heat Transfer Calculations Q: change in Heat m: mass (kg) C: Specific Heat T: Temperature (K)

Specific Heat is the amount of energy that must be added to the material to raise the temperature of a unit mass one temperature unit.

A.4000 kg block of iron is heated from 295 K to 325 K. How much heat had to be transferred to the iron?

What is the change in temperature of a 2.0 kg block of brass if 985 kJ of energy is added.

When phases change. Heat of fusion: that amount of energy needed to melt one kilogram of a substance. Heat of vaporization: the thermal energy need to vaporize one kilogram of a liquid.

You are asked to melt kg of ice at its melting point and warm the resulting water to 20.0 o C How much heat is needed?

How much heat is absorbed by 32.0 g of ice at o C to become water at 0.0 o C?

A solid substance with a mass of 200g is at its melting point temperature in a calorimeter. While the substance changes from a solid to a liquid at the same temperature, the g of water in the calorimeter goes from a initial temperature of 80.0 o C to a final temperature of 30.0 o C. What is the heat of fusion of the substance.

Relationships between heat and work: –Heat can be used to do work: Work can transfer energy to a substance, which increases the internal energy of the substance –Energy can be transferred to a substance as heat and form the substance as work

Heat and work are energy transferred to or from a system –System: a collection of matter with in a clearly defined boundary across with no matter passes. –Environment: everything outside a system that can affect or be affected by the system’s behavior.

Calculating the work done by a gas at constant pressure. An engine cylinder has a cross- sectional area of.010 m 2. How much work can be done by a gas in the cylinder if the gas exerts a constant pressure of 7.5x10 5 on the piston and moves the piston a distance of m.

Gas in a container is at a pressure of 1.6x10 5 and a volume of 4.0m 3. What is the work done by the gas if (a) it expands at constant pressure to twice it initial volume? (b) It is compressed at constant pressure to one-quarter of its initial volume?

Thermodynamic Processes: –Isovolumetric process: a thermodynamic process that takes place at constant volume so that no work is done on or by the system –Isothermal process: a thermodynamic process that takes place at constant temperature and is which the internal energy of a system remains unchanged.

–Adiabatic process: a thermodynamic process during which work is done on or by the system but no energy is transferred to or form the system as heat.

The First Law of Thermodynamics –The change in a systems internal energy equals energy transferred to or form system as heat minus energy transferred to or form system as work

Q>0Energy added to system as heat Internal energy increases if W=0 Q<0Energy is removed from system as heat Internal energy decreases if W=0 Q=0No transfer of energy as heat No internal energy changes if W=0

W>0Work is done by the system (gas expansion) Internal energy decreases if Q=0 W<0Work done on system (compression of gas) Internal energy increases if Q=0 W=0No work doneNo internal energy change if Q=0

Isovolumetric Systems –No work is done –ΔV=0, so PΔV=0 and W=0 therefore ΔU=Q –Interperetation: Energy added to the system as heat (Q>0) increases the systems internal energy. Energy removed form the system as heat (Q<0) decreases the system’s internal energy

Isothermal Processes –No change in temperature and internal energy –ΔT=0, so ΔU=0; therefore, –ΔU=Q-W=0 or Q=W –Interpretation: energy added to the system as heat is removed from the system as work done by the system Energy added to the system by work done on the system is removed from the system as heat.

Adiabatic Systems –No energy transferred as heat –Q=0 so ΔU=-W –Interpertation: Work done on the system (W 0) decreases the system’s internal energy.

Isolated Systems –No heat or work interactions with surroundings –Q=W=0, so ΔU=0 and U i =U f –Interpretation: There is no change in the system’s internal energy.

A total of 135 J of work is done on a gaseous refrigerant as it undergoes compression. If the internal energy of the gas increases by 114 J during the process, what is the total amount of energy transferred as heat? Has energy been added to or removed form the refrigerant as heat?