A 1.50-kg iron horseshoe initially at 680°C is dropped into a bucket containing 19.5 kg of water at 21.0°C. What is the final temperature of the water–horseshoe system? Ignore the heat capacity of the container and assume a negligible amount of water boils away. The water will gain the energy lost by the iron. Using the expressions for the quantity of heat exchanged by the two materials, the change in water temperature can be found. The specific heat of iron is 448 J/kg·°C and the specific heat of water is 4,186 J/kg·°C. We assume that the water–horseshoe system is thermally isolated (insulated) from the environment for the short time required for the horseshoe to cool off and the water to warm up. Then the total energy input from the surroundings is zero, as expressed by the equation Qiron + Qwater = 0. The energy Q transferred between a sample of mass m of a material and its surroundings with a temperature change ΔT is given by Q = mcΔT. Substituting the expressions for iron and water into the energy equation, we have (mcΔT)iron + (mcΔT)water = 0 or, with T as the final temperature of both the iron and the water, mironciron T − °C + mwatercwater T − °C = 0. Note that the first term in this equation results in a negative number of joules, representing energy lost by the originally hot horseshoe, and the second term is a positive number with the same absolute value, representing energy gained in heat by the colder water.
Energy transfer
The flow of energy from one region to another region is referred to as energy transfer. Since energy is quantitative; it must be transferred to a body or a material to work or to heat the system.
Molar Specific Heat
Heat capacity is the amount of heat energy absorbed or released by a chemical substance per the change in temperature of that substance. The change in heat is also called enthalpy. The SI unit of heat capacity is Joules per Kelvin, which is (J K-1)
Thermal Properties of Matter
Thermal energy is described as one of the form of heat energy which flows from one body of higher temperature to the other with the lower temperature when these two bodies are placed in contact to each other. Heat is described as the form of energy which is transferred between the two systems or in between the systems and their surrounding by the virtue of difference in temperature. Calorimetry is that branch of science which helps in measuring the changes which are taking place in the heat energy of a given body.
A 1.50-kg iron horseshoe initially at 680°C is dropped into a bucket containing 19.5 kg of water at 21.0°C. What is the final temperature of the water–horseshoe system? Ignore the heat capacity of the container and assume a negligible amount of water boils away.
The water will gain the energy lost by the iron. Using the expressions for the quantity of heat exchanged by the two materials, the change in water temperature can be found. The specific heat of iron is 448 J/kg·°C and the specific heat of water is 4,186 J/kg·°C.
We assume that the water–horseshoe system is thermally isolated (insulated) from the environment for the short time required for the horseshoe to cool off and the water to warm up. Then the total energy input from the surroundings is zero, as expressed by the equation
| Qiron + Qwater | = | 0. |
The energy Q transferred between a sample of mass m of a material and its surroundings with a temperature change ΔT is given by
| Q | = | mcΔT. |
Substituting the expressions for iron and water into the energy equation, we have
| (mcΔT)iron + (mcΔT)water | = | 0 |
or, with T as the final temperature of both the iron and the water,
| mironciron
|
= | 0. |
Note that the first term in this equation results in a negative number of joules, representing energy lost by the originally hot horseshoe, and the second term is a positive number with the same absolute value, representing energy gained in heat by the colder water.
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