The SI-unit of heat - or energy - is joule (J). Show With temperature difference Other units used to quantify heat are the British Thermal Unit - Btu (the amount of heat to raise 1 lb of water by 1oF) and the Calorie (the amount of heat to raise 1 gram of water by 1oC (or 1 K)).
A calorie is defined as the amount of heat required to change the temperature of one gram of liquid water by one degree Celsius (or one degree Kelvin).
Heat Flow (Power)Heat-transfer as result of temperature difference alone is referred to as heat flow. The SI units for heat flow is J/s or watt (W) - the same as power. One watt is defined as 1 J/s. Specific EnthalpySpecific Enthalpy is a measure of the total energy in a unit mass. The SI-unit commonly used is J/kg or kJ/kg. The term relates to the total energy due to both pressure and temperature of a fluid (such as water or steam) at any given time and condition. More specifically enthalpy is the sum of internal energy and work done by applied pressure. Heat CapacityHeat Capacity of a system is
Specific HeatSpecific heat (= specific heat capacity) is the amount of heat required to change temperature of one mass unit of a substance by one degree. Specific heat may be measured in J/g K, J/kg K, kJ/kg K, cal/gK or Btu/lboF and more. Never use tabulated values of heat capacity without checking the unites of the actual values!
Specific heat for common products and materials can be found in the Material Properties section. Specific Heat - Constant PressureThe enthalpy - or internal energy - of a substance is a function of its temperature and pressure. The change in internal energy with respect to change in temperature at fixed pressure is the Specific Heat at constant pressure - cp. Specific Heat - Constant VolumeThe change in internal energy with respect to change in temperature at fixed volume is the Specific Heat at constant volume - cv. Unless the pressure is extremely high the work done by applied pressure on solids and liquids can be neglected, and enthalpy can be represented by the internal energy component alone. Constant-volume and constant-pressure heats can be said to be equal. For solids and liquids
The specific heat represents the amount of energy required to raise 1 kg of substance by 1oC (or 1 K), and can be thought of as the ability to absorb heat. The SI units of specific heats are J/kgK (kJ/kgoC). Water has a large specific heat of 4.19 kJ/kgoC compared to many other fluids and materials.
Amount of Heat Required to Rise TemperatureThe amount of heat needed to heat a subject from one temperature level to an other can be expressed as:
Example Heating Water Consider the energy required to heat 1.0 kg of water from 0 oC to 100 oC when the specific heat of water is 4.19 kJ/kgoC:
WorkWork and energy are from a technical viewpoint the same entity - but work is the result when a directional force (vector) moves an object in the same direction. The amount of mechanical work done can be determined by an equation derived from Newtonian mechanics
Work can also be described as the product of the applied pressure and the displaced volume:
Example - Work done by a ForceThe work done by a force 100 N moving a body 50 m can be calculated as W = (100 N) (50 m) = 5000 (Nm, J) The unit of work is joule, J, which is defined as the amount of work done when a force of 1 newton acts for a distance of 1 m in the direction of the force.
Example - Work due to Gravitational ForceThe work done when lifting a mass of 100 kg an elevation of 10 m can be calculated as W = Fg h = m g h = (100 kg) (9.81 m/s2) (10 m) = 9810 (Nm, J) where Fg = force of gravity - or weight (N) g = acceleration of gravity 9.81 (m/s2) h = elevation (m) In imperial units a unit work is done when a weight of 1 lbf (pound-force) is lifted vertically against gravity through a distance of 1 foot. The unit is called lb ft. An object with mass 10 slugs is lifted 10 feet. The work done can be calculated as W = Fg h = m g h = (10 slugs) (32.17405 ft/s2) (10 feet) = 3217 lbf ft Example - Work due to Change in VelocityThe work done when a mass of 100 kg is accelerated from a velocity of 10 m/s to a velocity of 20 m/s can be calculated as W = (v22 - v12) m / 2 = ((20 m/s)2 - (10 m/s)2) (100 kg) / 2 = 15000 (Nm, J) where v2 = final velocity (m/s) v1 = initial velocity (m/s) EnergyEnergy is the capacity to do work (a translation from Greek-"work within"). The SI unit for work and energy is the joule, defined as 1 Nm. Moving objects can do work because they have kinetic energy. ("kinetic" means "motion" in Greek). The amount of kinetic energy possessed by an object can be calculated as
The energy of a level position (stored energy) is called potential energy. This is energy associated with forces of attraction and repulsion between objects (gravity). The total energy of a system is composed of the internal, potential and kinetic energy. The temperature of a substance is directly related to its internal energy. The internal energy is associated with the motion, interaction and bonding of the molecules within a substance. The external energy of a substance is associated with its velocity and location, and is the sum of its potential and kinetic energy.
calorie, abbr. cal, unit of heat energy in the metric system. The measurement of heat is called calorimetry. The calorie, or gram calorie, is the quantity of heat required to raise the temperature of 1 gram of pure water 1°C. The kilocalorie, or kilogram calorie, is the quantity of heat required to raise the temperature of 1 kg of pure water 1°C; it is equal to 1,000 cal. The kilocalorie is used in dietetics for stating the heat content of a food, i.e., the amount of heat energy that the food can yield as it passes through the body; in this context, the kilocalorie is usually called simply the calorie. The amount of heat energy needed to effect a 1°C temperature increase in 1 gram of water varies with temperature (see heat capacity); thus the temperature range over which the heating takes place must be stated to define the calorie precisely. The 15° calorie, or normal calorie, is widely used in chemistry and physics; it is measured by heating a 1-gram water sample from 14.5°C to 15.5°C at 1 atmosphere pressure. The 4° calorie, also called the small calorie or therm, is measured from 3.5°C to 4.5°C (water is most dense at 3.98°C); the large calorie, or Calorie, is equivalent to 1,000 small calories. The average value of the calorie in the range 0°C to 100°C is called the mean calorie; it is 1⁄100 of the energy needed to heat 1 gram of water from its melting point to its boiling point. The calorie may also be defined by expressing its value in some other energy units. The 15° calorie is equivalent to 4.185 joules (J), 1.162×10−6 kilowatt-hours, 3.968×10−3 British thermal units, and 3.087 foot-pounds; the 4° calorie equals 4.204 J; and the mean calorie equals 4.190 J. Two other calories sometimes used are the International Steam Table calorie, equal to 4.187 J, and the thermochemical calorie, equal to 4.184 J. When the calorie is used for precision measurement of heat energy, the particular calorie being used must be specified. The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2022, Columbia University Press. All rights reserved. See more Encyclopedia articles on: Physics |
What is the amount of heat required to raise the temperature of 1 gram of pure water through 1 0 C?
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