How much energy is required to raise the temperature of 12.6 grams of solid iodine from 21.3 °C to 36.1 °C ? In Joules

Answer 1

Hi Ally,

As a precursor to this question, note that the temperature of a solution, or compound, is a measure of the average internal kinetic energy of the atoms/molecules of which it is composed. The formula that relates the energy and temperature to each other is:

delta_Q = m*C*delta_T,

where delta_Q is the change in internal heat energy (sometimes delta_Q is just written as Q, but it really should be shown as delta_Q, as this equation tells us how much the internal energy of a compound changes when undergoing a change in temperature), m is the mass of the compound, C is the specific heat of the compound, and delta_T = T_final - T_initial is the change in temperature of the compound.

In the given problem, you are given the mass m, the initial and final temperatures required to find delta_T, and you can look up the value of C, the specific heat for solid iodine. (Note that differing sources for the values of C for differing compounds can vary, so use the values shown in your text to be sure your answers match theirs.)

A few things to be careful with when using this formula:

1: the specific heat C of a compound depends on the phase (solid, liquid, or gas), so be sure to pick the value that corresponds to solid iodine in this case,

2: be mindful of the units the values of C are given in, and be sure to convert the problems given unit values of m, and T to match, if necessary. The energy units for C are typically J or kJ, for mass are g or kg, and for T degrees Celsius or K--in the case of T, though the units of degrees Celsius and Kelvin are different, the difference delta_T between two temperatues in either unit will match. Also kJ / kg = J / g.

3: As mentioned previously, the values of C depend on the phase of the compound. If the change in temperature causes the compound to change phase (for example, water changing from a liquid to a gas as T foes from 90 C to 110 C, then there will be more steps required to find the change in energy delta_Q.

4: delta_Q may be positive or negative, and will match the sign of delta_T. Thus, when T goes up, and delta_T is positive, delta_Q will be positive, corresponding to an increase in internal energy of the compound. Similarly, a decrease in T corresponds to a loss of internal energy of the compound.

Hopefully, this answer helps. If you still have follow up questions, I recommend setting up a session to discuss these ideas in more detail.

Regards,

John Reese