Heat of Fusion, Heat of Vaporization, Specific Heat Table of Some Materials

		Specific Heat		Heat of Fusion	Heat of Vaporization
Material		(cal/g °C)		(cal/g)	(cal/g)
Aluminum		0.215		94.5
Copper		0.092		49.0
Iron		0.107		63.7
Lead		0.031		5.5	205
Brass		0.092		Unknown
Magnesium		0.245		88.0
Zinc		0.093		27.0
Styrofoam		0.27		Unknown
Air		0.240		N/A
Water		1.000		80.0	540
Ice		0.500		79.7
Oxygen				3.3	51
Nitrogen				6.1	48
Alcohol				26.0	204
Silver				26.5	563
methane				13.96
ethane				22.73
propane				19.11
methanol				23.70
ethanol			26.05
glycerol			47.95
formic acid			66.05
acetic acid			45.91
acetone			23.42
benzene			30.45
myristic acid			47.49
palmitic acid			39.18
stearic acid			47.54
nickel	0.106

Thermodynamics - Chemistry HW

A thermochemical equation is a balanced stoichiometric chemical equation which shows both mass relationships and enthalpy change (delta H) between products and reactants. In variable form, a thermochemical equation would look like this:

A + B → C

ΔH = (±) #

Where {A, B, C} are the usual agents of a chemical equation with coefficients and “(±) #” is a positive or negative numerical value, usually with units of kJ.

 

     An endothermic reaction refers to a chemical reaction in which a system receives heat from its environment. They must absorb energy in order to proceed. They cannot occur spontaneously. They are characterized by positive heat flow (into the reaction) and an increase in enthalpy (+ΔH). The endothermic chemical reaction creates a product that has a higher energy level than the original materials, causing the reactant's stored energy to decrease. The resulting product of the reaction is less stable because, the higher the energy bond, the less strength its molecules possess.

     It is the opposite of an endothermic reaction.

 

Exothermic reactions refers to chemical reactions which release energy in the form of heat, light, or sound. They may occur spontaneously and result in higher randomness or entropy of the system. They are denoted by a negative heat flow (heat is lost to the surroundings) and decrease in enthalpy. The reactants contain more stored energy than the product because energy from external sources is not required, but given off. This gives the product more stability due to the lower amount of energy needed.

 

At a more advanced level, heat change is called the enthalpy change. It is denoted by delta H, ΔH.

Enthalpy is considered as the heat content of the system.

ΔH represents the difference between the enthalpy of the system before and after the process and is represented as :

• ΔH is negative (-ve) for exothermic reactions i.e. heat energy is given out and lost from the system to the surroundings which warm up.
• ΔH is positive (+ve) for endothermic reactions i.e. heat energy is gained by the system and taken in from the surroundings which cool down OR, as is more likely, the system is heated to provide the energy needed to effect the change.

                                                                               

     The first law of thermodynamics, often called as the law of conservation of energy, states that energy can be transformed, but cannot be created nor destroyed. This law suggests that energy can be transferred from one system to another in many forms. The amount of energy in the universe is constant – merely changing from one form to another. However, this energy cannot be created from nothing or reduced to nothing. Every natural process transforms energy and moves energy, but cannot create or eliminate it.

     It is usually formulated by stating that the total energy lost by the system is equal to the total energy absorbed by its surroundings. Likewise, the total energy absorbed by the system is equal to the energy lost bythe surroundings.

Physical Changes; Heat of Fusion, Heat of Vaporization, Specific Heat; Heat - Chemistry HW

PHYSICAL CHANGES

Melting or fusion is a process that results in the phase change of a substance from a solid to a liquid. The internal energy of a substance is increased as heat goes into the solids as it melts, resulting in a rise of its temperature to the melting point, at which the rigid ordering of molecular entities in the solid breaks down to a less-ordered state and the solid liquefies.

Freezing or solidification is a phase change in which a liquid turns into a solid when its temperature is lowered below its freezing point. Heat leaves the liquid as it freezes.

Vaporization is the change of state from liquid to gas. Heat goes into the liquid as it vaporizes.

Condensation is the change of state from gas to liquid. Heat leaves the gas as it condenses.

Sublimation is the conversion of a solid directly into a gas without passing through an intermediate liquid phase. Heat goes into the solid as it sublimes.

Deposition or desublimation is a process in which gas transforms into solid. Heat leaves the gas as it solidifies.

*****************************************************************************************************

Heat of fusion is the amount of necessary heat absorbed by one mole of a substance to convert a given amount of a solid into a liquid.  This energy is required to separate the solid particles. It results in the higher potential energy of the liquid as compared with that of the solid.

Heat of Vaporization is the amount of necessary heat absorbed by one mole of a substance to change a given amount of a liquid at its boiling point into a gas.

Specific Heat is the heat capacity of 1 gram of a substance. It is a physical property of a substance. It is the amount of heat that must be absorbed or lost per unit mass required to change the temperature by one degree Celsius.

*****************************************************************************************************

The molar heat of fusion equation looks like this:

q = ΔH_fus (mass/molar mass)

The meanings are as follows:

1) q is the total amount of heat involved
2) ΔH_fus is the symbol for the molar heat of fusion. This value is a constant for a given substance.
3) (mass/molar mass) is the division to get the number of moles of substance

The molar heat of vaporization equation looks like this:

q = ΔH_vap (mass/molar mass)

The meanings are as follows:

1) q is the total amount of heat involved
2) ΔH_vap is the symbol for the molar heat of vaporization. This value is a constant for a given substance.
3) (mass/molar mass) is the division to get the number of moles of substance

Q=c_pmΔT

Q is the amount of heat needed to change the temperature of a substance
m is the mass of the heated substance
cp is the specific heat capacity

ΔT (pronounced delta T) is the temperature difference; the difference in temperature before and after you applied the heat

***************************************************************************************************** 

MOST COMMON UNITS FOR HEAT

BTU - British Thermal Unit

The unit of heat in the imperial system - the BTU - is

• the amount of heat required to raise the temperature of one pound of water through 1^oF (58.5^oF - 59.5^oF) at sea level (30 inches of mercury).
• 1 Btu (British thermal unit) = 1055.06 J = 107.6 kpm = 2.931 10^-4 kWh = 0.252 kcal = 778.16 ft.lbf = 1.05510¹⁰ ergs = 252 cal = 0.293 watt-hours

An item using one kilowatt-hour of electricity generates 3412 Btu.

Calorie

A calorie is commonly defined as

• the amount of heat required to raise the temperature of one gram of water 1^oC
• the kilogram calorie, large calorie, food calorie, Calorie (capital C) or just calorie (lowercase c) is the amount of energy required to raise the temperature of one kilogram of water by one degree Celsius
• 1 kcal = 4186.8 J = 426.9 kp.m = 1.163 10^-3 kWh = 3.088 ft.lbf = 3.9683 Btu = 1000 cal

Be aware that alternative definitions exists - in short: 

• Thermochemical calorie  
• 4 °C calorie
• 15 °C calorie
• 20 °C calorie
• Mean calorie
• International Steam Table calorie (1929)
• International Steam Table calorie (1956)
• IUNS calorie (Committee on Nomenclature of the International Union of Nutritional Sciences)

The calorie is outdated and commonly replaced by the SI-unit Joule.

Joule

The unit of heat in the SI-system the Joule is

• a unit of energy equal to the work done when a force of one newton acts through a distance of one meter
• 4.184 joule of heat energy (or one calorie) is required to raise the temperature of a unit weight (1 g) of water from 0^oC to 1^oC, or from 32^oF to 33.8^oF
• 1 J (Joule) = 0.1020 kpm = 2.778 10^-7 kWh = 2.389 10^-4 kcal = 0.7376 ft.lbf = 1 kg.m²/s² = 1 watt second = 1 Nm = 1 ft.lb = 9.478 10^-4 Btu