What Is Kj In Chemistry

How To Calculate Joules Of Heat

Back in the early 19th century, a British brewer and physicist named James Joule demonstrated that heat and mechanical work were two forms of the same thing: energy. His discovery earned him a lasting place in science history today, the unit in which energy and heat are measured is named after him. You can easily calculate the amount of heat absorbed or released by an object as long as you know three things: its mass, the change in its temperature, and the type of material it’s made from.

TL DR

TL DR

Calculate the joules of heat absorbed or released using the formula:

Heat = mass of object × change in temperature × specific heat capacity of material

Look up the specific heat capacity of your material. The first link under the resources section lists the specific heat capacities of common solids the second link lists the heat capacities of common liquids. Use the value under the column with units of kJ/kg K. Note that kJ stands for kilojoule, one thousand joules, while kg is a kilogram, a unit of mass, and K is Kelvin, a unit of temperature. A change of one degree Kelvin is equal to a change of one degree Centigrade.

Subtract the starting temperature of your object from its final temperature to find the change in temperature. If your change in temperature is in Fahrenheit, convert it to degrees Kelvin by using the following formula:

× 5/9 = temperature in Celsius

Answer: The specific heat capacity of water is 4.184 kilojoules / kg K.

× × = 1673.6 kilojoules.

What Happens If You Eat Too Many Kilojoules

eating too many kilojoulesWhen weeatkilojoulesEatingcan

Here are eight possible ways to burn more calories and fight fat:

Examples Of Kilojoule In A Sentence

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These example sentences are selected automatically from various online news sources to reflect current usage of the word ‘kilojoule.’ Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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Worked Examples Of Converting Calories To Joules And Joules To Calories

Question 1: Convert 100 calories to joules

Solution:

multiply both sides of the equation by 100:

100 × 1 calorie = 100 × 4.18 J

100 cal = 418 J

Question 2: Convert 12.0 kilocalories to kilojoules

Solution:

multiply both sides of the equation by 12.0

12.0 × 1 kilocalorie = 12.0 × 4.18 kJ

12.0 kcal = 50.2 kJ

Question 3: Convert 150 kilocalories to joules

Solution:

Calculate the number of kilojoules in 150 kilocalories:

1 kilocalorie = 4.18 kilojoules

multiply both sides of the equation by 150

150 × 1 kilocalorie = 150 × 4.18 kJ

150 kcal = 627 kJ

Calculate the number of joules in 622 kJ

1 kilojoule = 1000 joules

multiply both sides of the equation by 622

627 × 1 kJ = 627 × 1000 J

627 kJ = 627 000 J

Write the answer to the question:

150 kcal = 627,000 J

Question 4: Convert 10 joules to calories

Solution:

multiply both sides of the equation by 10

10 × 1 J = 10 × 0.239 cal

10 J = 2.39 cal

Question 5: Convert 1.2 kilojoules to kilocalories

Solution:

multiply both sides of the equation by 1.2

1.2 × 1 kJ = 1.2 × 0.239 kcal

1.2 kJ = 0.287 kcal

Question 6: Convert 1500 joules to kilocalories

Solution:

Calculate the number of calories in 1500 joules

1 joule = 0.239 calories

multiply both sides of the equation by 1500

1500 × 1 J = 1500 × 0.239 cal

1500 J = 359 calories

Calculate the number of kilocalories in 539 calories

1000 calories = 1 kilocalorie

Divide both sides of the equation by 1000

1000

multiply both sides of the equation by 539

359 × 1 calorie = 359 × 0.001 kilocalories

What Does Kj Stand For Chemistry

We compiled queries of the KJ abbreviation in Chemistry in search engines. The most frequently asked KJ acronym questions for Chemistry were selected and included on the site.

We thought you asked a similar KJ question to the search engine to find the meaning of the KJ full form in Chemistry, and we are sure that the following Chemistry KJ query list will catch your attention.

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Free Energy And Equilibrium

The free energy change for a process may be viewed as a measure of its driving force. A negative value for G represents a finite driving force for the process in the forward direction, while a positive value represents a driving force for the process in the reverse direction. When G is zero, the forward and reverse driving forces are equal, and so the process occurs in both directions at the same rate .

In the chapter on equilibrium the reaction quotient, Q, was introduced as a convenient measure of the status of an equilibrium system. Recall that Q is the numerical value of the mass action expression for the system, and that you may use its value to identify the direction in which a reaction will proceed in order to achieve equilibrium. When Q is lesser than the equilibrium constant, K, the reaction will proceed in the forward direction until equilibrium is reached and Q = K. Conversely, if Q< K, the process will proceed in the reverse direction until equilibrium is achieved.

The free energy change for a process taking place with reactants and products present under nonstandard conditions, G, is related to the standard free energy change, G°, according to this equation:

R is the gas constant , T is the kelvin or absolute temperature, and Q is the reaction quotient. We may use this equation to predict the spontaneity for a process under any given set of conditions as illustrated in Example 5.

Standard Enthalpy Of Reaction

The standard enthalpy of reaction is the enthalpy of a reaction carried out at 1 atm. We have already learned one process by which we can calculate the Enthalpy of Reaction in Calorimetry. There are two other methods we will learn now:

1) Heat of Reaction from Standard Heats of Formation

2) Heat of Reaction from Hess’ Law Calculation

Calculation of the Heat of Reaction from Standard Heats of Formation is based on the following equations:

The Heat of Reaction can be calculated from the Heats of Formation of each molecule in the reaction. The equation shown above shows that the HoRxn value is calculated as the sum of the moles of the products times their HoF values minus the sum of the the moles of the reactants times their HoF values.

Hesss Law: When reactants are converted to products, the change in enthalpy is the same whether the reaction takes place in one step or in a series of steps. Remember that Enthalpy is a state function. It doesnt matter how you get there, only where you start and end.

Here is an example of how to complete a calculation of this type:

The third process by which you can calculate the Heat of a Reaction is by using a process called Hess’ Law. Another way to state Hess’ Law is The enthalpy change of an overall process is the sum of the enthalpy changes of its individual steps.

A couple of rules before we start:

The “target” reaction is S + 3/2 O2 SO3 H = ?

S + O2 SO2 H1 = -296.0 kJ

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What Does Kj Stand For

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Chapter 7 Energy And Chemistry

Energy: is the ability to do work. Think about it: when you have a lot of energy, you can do a lot of work but if youre low on energy, you dont want to do much work. Work itself is defined as a force operating over a distance :

w = F × x

In SI, force has units of newtons , while distance has units of meters. Therefore, work has units of N·m. This compound unit is redefined as a joule :

1 joule = 1 newton·meter1 J = 1 N·m

Because energy is the ability to do work, energy is also measured in joules. This is the primary unit of energy we will use here.

How much is 1 J? It is enough to warm up about one-fourth of a gram of water by 1°C. It takes about 12,000 J to warm a cup of coffee from room temperature to 50°C. So a joule is not a lot of energy. It will not be uncommon to measure energies in thousands of joules, so the kilojoule is a common unit of energy, with 1 kJ equal to 1,000 J.

An olderbut still commonunit of energy is the calorie. The calorie was originally defined in terms of warming up a given quantity of water. The modern definition of calorie equates it to joules:

1 cal = 4.184 J

Figure 7.1 Calories on Food Labels

This label expresses the energy content of the food, but in Calories .Source: FDA Nutrition Facts Label 2014 by U.S. Food and Drug Administration is in the public domain.

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Worked Examples Of Converting Joules To Kilojoules And Kilojoules To Joules

Question 1: Convert 1 kilojoule to joules

Solution:

From the table above we see that kilo = 103 = 1,000

1 kJ = 103 J = 1,000 J

1 kilojoule = 1,000 joules

Question 2: Convert 2.5 kJ to joules

Solution:

From the table above we see that kilo = 103 = 1,000

1 kJ = 1,000 J

Multiply both sides of equation by 2.5:

2.5 × 1 kJ = 2.5 × 1,000 J

2.5 kJ = 2,500 J

Which we can express in scientific notation as:

2,500 J = 2.5 × 103 J

Question 3: Convert 5 millijoules to joules

Solution:

From the table above we see that milli = 10-3

1 mJ = 10-3 J

Multiply both sides of the equation by 5:

5 × 1 mJ = 5 × 10-3 J = 0.005 J

5 mJ = 0.005 J

Question 4: Convert 250 J to kilojoules

Solution:

From the table above we see that:

103 J = 1 kJ

Divide both sides of the equation by 1000 to find the number of kilojoules in 1 joule:

1 J = 10-3 kJ = 0.001 kJ

Multiply both sides of the equation by 250:

250 × 1 J = 250 × 0.001 kJ

250 J = 0.250 kJ

Question 5: Convert 25 µJ to kilojoules

Solution:

From the table above we see tha µ = 10-6

1 µJ = 10-6 J

Multiply both sides of this equation by 25 to determine the number of joules in 25 µJ :

25 × 1 µJ = 25 × 10-6 J

25 µJ = 2.5 × 10-5 J

Convert 2.5 × 10-5 J to kilojoules:

From the table above we see that:

1 kJ = 103 J

Divide both sides of this equation by 103:

1 kJ ÷ 103 = 1 J ÷ 103

10-3 kJ = 1 J

Multiply both sides of the equation by 2.5 × 10-5 to find the number of kJ in 2.5 × 10-5 J

× 10-3 kJ = × 1 J

2.5 × 10-8 kJ = 2.5 × 10-5 J

State the answer to the question:

Difference Between Kj And Kcal

June 6, 2018 Posted by Madhu

The key difference between KJ and KCal is that KJ is the unit of measuring the energy content of a substance or a chemical reaction using joules whereas KCal is the unit measuring the energy content of a substance regarding calories.

Both KJ and KCal are units that are useful in expressing the energy content of a substance or a chemical reaction. The prefix K in both these terms refers to kilo which means, these terms give the energy content in 103 portions.

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Calculating Free Energy Change

Free energy is a state function, so its value depends only on the conditions of the initial and final states of the system that have undergone some change. A convenient and common approach to the calculation of free energy changes for physical and chemical reactions is by use of widely available compilations of standard state thermodynamic data. One method involves the use of standard enthalpies and entropies to compute standard free energy changes according to the following relation as demonstrated in Example 1.

Joules To Kj/mol Conversion

In my AP Chem class we are working on testing Hess’s Law and conducted three reactions. Then enthalpy changes of the 1) $\ce$ and 2) $\ce$ to predict the enthalpy change of 3) $\ce$.

I used the equation $q = C_pm\Delta T$. We determined the $q$-values using a method given to us by our teacher. She told us to assume a denisty of $1.03\ \mathrm$ for all solutions, we then multiplied the density by $50\ \mathrm$ to determine the grams of each reactant present. That value is the $m$ term. We used $4.18\ \mathrm$ for the specific heat of water. The temperature change for the first reaction was $14.7\ \mathrm$, the second was $1.2\ \mathrm$, and the third was $9.8\ \mathrm$.

The first reaction yielded a q value of $6328.938\ \mathrm J$, the second yielded $516.648\ \mathrm J$, and the third yielded $4219.292\ \mathrm J$.

The next step would be to convert this $q$ values into $\mathrm$. I consulted my lab partner who did the following operation:

$$\mathrm = 6328.938\ \mathrm J \times 1\ \mathrm/1000\ \mathrm J \times x/0.2\ \mathrm$$

In his math, there was no numerator on the $0.2\ \mathrm$ term. The mol value he used came from there being 0.2 moles of the reactants present. I believe his math to be incorrect, but as my teacher is out sick and there are no other chemistry teachers present, I cannot determine the correct conversion. I believe it to be:

$$\mathrm = 6328.938\ \mathrm J \times 1\ \mathrm/1000\ \mathrm J \times 6.022^/0.2\ \mathrm$$

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Lesson Explainer: Units Of Energy Chemistry

In this explainer, we will learn how to express energy in different units and convert between them.

Energy is the capacity for doing work. There are different categories of energy some of them include electric potential energy, chemical potential energy, kinetic energy, and gravitational potential energy.

What Are Kilojoules Chemistry

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Subsequently, one may also ask, what are kilojoules?

kJ is the Australian measure of how much energy people get from consuming a food or drink. Energy in food and drinks is measured by the number of kJ it provides. kJ are similar to Calories: 1 kJ = 0.2 Calories 1 Calorie = 4.2 kJs.

Also Know, what is the difference between kilojoules and calories? Essentially, the difference between calories and kilojoules is terminology – they’re two different ways of measuring the energy contained in food and the energy we expend. You can convert calories to kilojoules by multiplying the calories by 4.2.

Furthermore, what are calories in chemistry?

A calorie is a unit of thermal energy equal to 4.184 joules or the amount of energy required to raise the temperature of 1 gram of liquid water 1°C at standard pressure.

How are kilojoules measured?

A kilojoule is a unit of measure of energy, in the same way that kilometres measure distance. Food energy used to be measured in Calories and some countries still use those units. The conversions are as follows: 1 kJ = 0.2 Cal.

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Definition: International System Of Units

It is a set of seven standardized base units derived from the seven fundamental constants. The SI units are the metre , kilogram , second , ampere , kelvin , mole , and candela .

The joule is represented with a single uppercaseJ letter. A joule is defined as the amount of thermal energy required to raise the temperature of 1 g of water by 1

A joule is an extremely small amount of energy, and we regularly expend and consume much larger quantities of energy when we eat and move. It is usually more appropriate to describe energy with the kilojoule unit. The energy contained in a single slice of bread is approximately 250000 J of energy! This is a very large number, and most nutritionists would choose to express this value as 250 kJ.

We can use the following relationship to convert between joule and kilojoule units.

The relationship shows that joules can be divided by 1000 to determine the same value in kilojoules . The relationship also shows that kilojoules can be multiplied by 1000 to determine the same value in joules. 250000 J can be divided by 1000 to express it as a value of 250 kJ.

The following conversion factors can also be used to convert between the joule and kilojoule units: 1

The unit conversion factor is appropriate here as the units of J will cancel out, leaving only units of kJ.