Heat capacity, of water

Taking the heat capacity of water to be 4.3 kJ kg K , heat duty on boiler feedwater preheating is... 

Different areas of the earth s surface react quite differently to heating by the sun. For example, although a sandy surface reaches fairly high temperatures on a sunny day, the heat capacity and conductivity of Scmd are relatively low the heat does not penetrate more than about 0.2-0.3 m and little heat is stored. In contrast, in a body of water, the sun s rays penetrate several meters and slowly heat a fairly deep layer. In addition, the water can move readily and convection can spread the heat through a deeper layer. The heat capacity of water is considerably greater than that of sand. All these factors combine to allow considerable storage of heat in water bodies. 

The heat capacity of a subshince is defined as the quantity of heat required to raise tlie temperature of tliat substance by 1° the specific heat capacity is the heat capacity on a unit mass basis. The term specific heat is frequently used in place of specific heat capacity. This is not strictly correct because traditionally, specific heal luis been defined as tlie ratio of the heat capacity of a substance to the heat capacity of water. However, since the specific heat of water is approxinuitely 1 cal/g-°C or 1 Btiiyib-°F, the term specific heal luis come to imply heat capacity per unit mass. For gases, tlie addition of heat to cause tlie 1° tempcniture rise m iy be accomplished either at constant pressure or at constant volume. Since the mnounts of heat necessary are different for tlie two cases, subscripts are used to identify which heat capacity is being used - Cp for constant pressure or Cv for constant volume. Tliis distinction does not have to be made for liquids and solids since tliere is little difference between tlie two. Values of heat capacity arc available in the literature. ... 

In all of these systems, by definition, the specific heat capacity of water is unity. It may be noted that, by comparing the definitions used in the SI and the mks systems, the kilocalorie is equivalent to 4186.8 J/kg K. This quantity has often been referred to as the mechanical equivalent of heat J. 

In the region of supercritical point, most properties of supercritical water vary widely. The most prominent of these is the heat capacity at constant pressure, which approaches infinity at the critical point. Even 25°C above Tc, at 80 bar away from Pc, the heat capacity of water is an order of magnitude greater than its value at higher or lower pressure. 

Calculate the specific enthalpy of water at a pressure of 1 bar and temperature of 200 °C. Check your value using steam tables. The specific heat capacity of water can be calculated from the equation ... 

EXAMPLE 18.10. What is the final temperature of 2.25 mol of water initially at 17.l°C from which 1910J of heat is removed The molar heat capacity of water is 75.38 J/mol deg. 

Assuming that radiation losses amount to 20 kJ/kg of dry air used, determine the mass flow of dry air supplied to the dryer and the humidity of the outlet air. The latent heat of water vapour at 295 K = 2449 kJ/kg, the specific heat capacity of dried material = 0.88 kJ/kg K, the specific heat capacity of dry air = 1.00 kJ/kg K, and the specific heat capacity of water vapour = 2.01 kJ/kg K. 

Analysing Equations (3.6) and (3.7) helps us remember how the SI unit of heat capacity Cy is J K-1. Chemists usually cite a heat capacity after dividing it by the amount of material, calling it the specific heat capacity, either in terms of J K-1 mol-1 or J K-1g-1. As an example, the heat capacity of water is 4.18 J K-1g-1, which means that the temperature of 1 g of water increases by 1 K for every 4.18 J of energy absorbed. 

The specific heat capacity commonly has units of J/g-K. The specific heat capacity of water is 4.18 J/g-K. If we have the specific heat capacity, the mass, and the change of temperature, it is possible to determine the amount of energy absorbed or released (q). 

The specific heat capacity of water is necessary to solve many problems. However, when reading the problem, it is often not apparent that you must use this value. If the problem mentions water, its specific heat capacity will often be part of the solution to the problem. 

From the steam tables in the Appendix, the latent heat of vaporisation of water at 312 K is 2410 kl/kg. Again from steam tables, the specific heat capacity of water vapour = 1.88 kJ/kg K and that of the solids will be taken as 2.18 kl/kg K. 

The chemist uses a coffee-cup calorimeter to neutralize completely 61.1 mL of 0.543 mol/L HCl(aq) with 42.6 mL of NaOH(aq). The initial temperature of both solutions is 17.8°C. After neutralization, the highest recorded temperature is 21.6°C. Calculate the enthalpy of neutralization, in units of kJ/mol of HCl. Assume that the density of both solutions is 1.00 g/mL. Also assume that the specific heat capacity of both solutions is the same as the specific heat capacity of water. 

The relatively high heat capacity of water has important consequences for climate and life on Earth. For example, seasonal changes in atmospheric temperatures are moderated at mid-latitudes via adsorption of heat by the ocean s surfece waters during the summer and release of this heat diudng the winter. Thus, mid-latitude coastal zones experience much smaller seasonal atmospheric temperature fluctuations than occur inland. 

However, some of these mine waters have significant potential for energy recovery via use of heat pumps. For example, the Morlais mine water of South Wales has an estimated discharge of at least 100 L/s. The specific heat capacity of water is around 4181 J/L/°C or 1.16kWh/m3/ °C. If the Morlais mine water s temperature could be lowered by using a heat pump by 5 °C (from 14 to 9 °C), a heat flux (power) of ... 

A 375 g plug of lead is heated and placed in an insulated container filled with 0.500 L of water. Prior to the immersion of the lead, the water is at 293 K. After a time, the lead and the water assume the same temperature, 297 K. The specific heat capacity of lead is 0.127 J/(g K), and the specific heat capacity of water is 4.18 J/(g K). How hot was the lead before it entered the water (Hint You ll need to use the density of water.)... 

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