# Need help with simple calorimetry problem

• kishin7
In summary, the problem is calculating the final temperature of a solution of CaCl2 and water, using the heat of solution and specific heat capacity of water. The heat capacity of the solution will be close to that of pure water, which is 4.18 J/(g*C). The correct formula to use is q(rxn) = q(water) + q(CaCl2), and the left side of the equation is not needed. The enthalpy of reaction is given in kJ/mole and will need to be converted to kJ. The energy from the reaction is used to raise the temperature of the solution. The specific heat capacity of 4.184 J/C*g applies specifically to water and not to the
kishin7
So here's the problem

Conside the dissolution of CaCl2:

CaCl2(s) ---> Ca^(2+) (aq) + 2Cl^(-1) (aq) deltaH = -81.5kJ

An 11.0g sample of CACl2 id dissolved in 125g of water, with both substances at 25.0°C. Calculate the final temperature of the solution assuming no heat lost to the surroundings and assuming the solution has a specific heat capacity of 4.18 J/(°C*g).

So far I think it's just q(rxn) = q(water) + q(CaCl2)

(136g)(4.184J/°Cg)(Tfinal - 25.0°C) = (125g)(4.184)(Tfinal - 25.0°c) + (11g)c(Tfinal - 25.0°C)

But it seems that I am missing C for the calcium chloride and I don't know what to do about it? is there another way to calculating it without C of CaCl2?

The heat capacity(Cp) of the solution will be very close to that of pure water, 4.18 J/(g C). The problem states this.

Are you suggesting that I use 4.184 for the heat capacity of every one? If I do then it wouldn't make sense since that's just making the left side equal to the right side and getting at final temperature of 25.0°C.

By the way, is my formula correct though?

heat of solution = heat of water + heat of calcium chloride

So far I think it's just q(rxn) = q(water) + q(CaCl2)

(136g)(4.184J/°Cg)(Tfinal - 25.0°C) = (125g)(4.184)(Tfinal - 25.0°c) + (11g)c(Tfinal - 25.0°C)
You won't need the left side of this equation. Note that the enthalpy is in kJ/mole of reaction. How would you convert kJ/mole of reaction to kJ?

This energy is equivalent to q...it is used to raise the temperature of ___?

"(136g)(4.184J/°Cg)(Tfinal - 25.0°C)",

this is incorrect, 4.184J/Cg applies specifically to water.

Last edited:

## 1. What is calorimetry?

Calorimetry is the science of measuring the amount of heat released or absorbed during a chemical reaction or physical process. It is typically done by using a device called a calorimeter, which measures the temperature change of a substance.

## 2. How does calorimetry work?

Calorimetry works by using the principle of energy conservation. The heat released or absorbed during a reaction is equal to the heat gained or lost by the surrounding environment. By measuring the temperature change of the surrounding environment, the amount of heat released or absorbed can be determined.

## 3. What is a simple calorimetry problem?

A simple calorimetry problem involves calculating the amount of heat released or absorbed during a reaction using basic calorimetry principles. This typically involves measuring the initial and final temperatures of the surrounding environment and using these values to calculate the change in heat.

## 4. What are the units for heat in a calorimetry problem?

The units for heat in a calorimetry problem are typically expressed in joules (J) or calories (cal). Joules are the standard unit of energy in the International System of Units (SI), while calories are commonly used in chemistry and nutrition.

## 5. How can I use calorimetry to solve a problem?

To solve a calorimetry problem, you will need to gather all the necessary information, such as the initial and final temperatures, the specific heat capacity of the substances involved, and any other relevant data. Then, you can use the basic calorimetry equation (q = m x c x ΔT) to calculate the change in heat and solve for the unknown variable.

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