# What Is Qcal?

## What is the heat combustion per gram of quinone?

A 2.200-g sample of quinone (C6H4O2) is burned in a bomb calorimeter whose total heat capacity is 7.854kJ/degree C. The temp of the calorimeter increases from 23.44C to 30.57C. Answer: -27.5kJ/g How do you get that answer?

My answer is just a bit different. qcal = Ccal ΔT; qw = Cw ΔT; qreaction = qcal + qw

Ccal = bomb calorimeter heat capacity = 7.854 kJ/degree C

Cw = heat capacity of water = 4.184 J

qcal = the heat flow for the calorimeter

qw = the heat flow for the water

ΔT = (30.57 C - 23.44 C) = 7.13 C

qcal = Ccal ΔT = 7.854 kJ/degree C(7.13 C) = 55.999 kJ

q from calorimeter = 55.999 kJ/2.200 g = 25.5 kJ/g

q from water = unknown because we don't know the mass of the water.

specific heat of water = sw = 4.184 J/C.g

Note: The q from calorimeter is +, so the q from the reaction is -. I suspect that the sum of the q from the calorimeter and q from the water is equal to 27.5 kJ so the heat of combustion of the 2.200 g of quinone will be -27.5 kJ/g. Since we don't know how much water was there we can't calculate the total heat of combustion.

Of course I could be wrong. You can let me through e-mail know if you want to.

## calorimetry(need help in acquiring net ionic eq, qrxn, qcal)?

in the reaction 10mL of 1M NaOH + 5mL of 1M HCl (adiabatic) given change in temp=2.1°C (temp initial is the temp of NaOH, temp final is acquired after the addition of HCl) find: net ionic equation, qrxn, qcal i want to check if my solutions are correct. so please show the solutions. thanks

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I am sorry, but it's too late to answer !

## What is the heat capacity of the calorimeter?

The heat of combustion of benzoic acid (C6H5COOH) is -3226 kJ/mol at constant volume. 0.864 grams of benzoic acid is burned in a bomb calorimeter. The temperature of the calorimeter (including its contents) rose from 24.01oC to 28.01oC. What is the heat capacity (calorimeter constant) of the calorimeter?

Heat Capacity of the Calorimeter

Concepts

In calorimetry it is often desirable to know the heat capacity of the calorimeter itself rather than the heat capacity of the entire calorimeter system (calorimeter and water). The heat (q) released by a reaction or process is absorbed by the calorimeter and any substances in the calorimeter. If the only other substance in the calorimeter is water, the following energy balance exists:

q = qcal + qw

where qcal is the heat flow for the calorimeter and qw is the heat flow for the water.

Both of these individual heat flows can be related to the heat capacity and temperature change for the substance.

qcal = Ccal ΔT

qw = Cw ΔT

where Ccal is the heat capacity of the calorimeter and Cw is the heat capacity of the water. Because the water and calorimeter are in thermal equilibrium, they both have the same temperature and thus ΔT is the same for both. The consequence is that the heat capacity of the entire system (C) is the sum of the heat capacities for the individual components.

C = Ccal + Cw

The heat capacity is an extensive property; that is, the heat capacity depends upon the amount of substance present. The calorimeter exists as a fixed unit, thus its heat capacity is a fixed value. The amount of water in the calorimeter, however, can vary, and thus the heat capacity of the water can vary. When dealing with variable amounts of material, one often prefers to use an intensive measure of the heat capacity. One common intensive version of the heat capacity is the specific heat capacity (s), which is the heat capacity of one gram of a substance.

sw = Cw

mw

Because the mass of water (mw) and the specific heat capacity of water are both known, one can readily calculate the heat capacity of the water. The joule (J) is defined based upon the specific heat capacity of water:

sw = 4.184 J oC-1 g-1

Overall one can write

C = Ccal + sw mw

Quantity Symbol Unit Meaning

heat q J Energy transfer that produces or results from a difference in temperature

temperature T oC or K Measure of the kinetic energy of molecular motiom

temperature change ΔT oC or K Difference between the final and initial temperatures for a process

mass m g Amount of material present

heat capacity C J oC-1 or J K-1 Heat required to change the temperature of a substance one degree

specific heat capacity s J oC-1 g-1 or J K-1 g-1 Heat required to change the temperature of one gram of a substance one degree

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