Chemistry for Engineers

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Questions and Answers

What does a calorimeter measure during a chemical reaction?

The energy change of the system (correct)

The temperature of the surroundings

The total pressure in the reaction

The amount of reactants used

Which statement is true regarding the change in enthalpy (ΔH)?

ΔH is always zero in chemical reactions

ΔH is positive for exothermic reactions

ΔH can be directly measured for reactants and products

ΔH describes heat change at constant pressure (correct)

In a constant pressure calorimeter, what happens to the heat lost by the chemicals?

It is gained by the solution (correct)

It is lost to the air surrounding the calorimeter

It does not affect the overall reaction

It is absorbed by the calorimeter itself

Which type of calorimeter maintains constant volume during a reaction?

Bomb calorimeter Signup and view all the answers

What is the relationship between heat absorbed by a solution and the heat released by the substance?

They are always equal Signup and view all the answers

What characterizes an exothermic reaction in terms of ΔH?

ΔH is negative Signup and view all the answers

Which of the following is NOT a reason for using a calorimeter?

To determine the exact enthalpy of reactants Signup and view all the answers

What does the symbol ΔH represent in thermodynamics?

Change in enthalpy Signup and view all the answers

What does the equation qsubstance = - qsolution signify in a calorimeter?

Heat gained by the solution is equal to heat lost by the substance Signup and view all the answers

How is the heat absorbed by the surroundings related to the heat released by the system?

They are equal but have opposite signs. Signup and view all the answers

In a constant pressure calorimeter, what does the equation qsurr = m x C x ΔT calculate?

Heat absorbed or released by the surroundings Signup and view all the answers

If the initial temperature of a substance is higher than its final temperature after a reaction, what can be inferred?

The substance released heat. Signup and view all the answers

What units are typically used for measuring specific heat capacity?

J/g·celsius Signup and view all the answers

What is the specific heat capacity of water used in calorimetry experiments?

4.184 J/g·celsius Signup and view all the answers

During a calorimetry experiment, what is the significance of achieving thermal equilibrium between two substances?

The temperature of both substances is the same. Signup and view all the answers

If 0.45 grams of copper is mixed with water, what must be ensured for the measurement to be accurate?

Heat loss to the environment must be negligible. Signup and view all the answers

What is the total heat gained by the water when the copper loses heat?

10.91 J Signup and view all the answers

What would be the mass of water that gained 10.91 J when its specific heat is 4.184 J/g°C?

2.61 grams Signup and view all the answers

If the final temperature of the water is 24 degrees Celsius, what is the temperature change (ΔT) experienced by the water?

3.0 degrees Celsius Signup and view all the answers

What is the relationship between the heat lost by the titanium and the heat gained by the water in the calorimeter?

Heat lost by titanium equals the heat gained by the water. Signup and view all the answers

To find the specific heat of titanium, what values would you need to consider from the scenario provided?

Mass, specific heat, and temperature change of both titanium and water. Signup and view all the answers

What would be the calculated heat (q) gained by the water if its mass is 75 grams, specific heat is 4.184 J/g°C, and it heats from 21.7 °C to 24.3 °C?

815.88 J Signup and view all the answers

What is the initial temperature of the titanium before it is added to the calorimeter containing water?

99.5 degrees Celsius Signup and view all the answers

If the heat lost by titanium is expressed as a negative value according to thermodynamic principles, what is the rationale behind this?

It represents heat is leaving the titanium. Signup and view all the answers

What is the specific heat capacity of titanium calculated in the experiment?

0.522 J/g degrees Celsius Signup and view all the answers

In the calorimetry experiment, what is the mass of ice used?

16.4 g Signup and view all the answers

What does the negative value of ∆H indicate in the heat of reaction calculations?

The reaction is exothermic. Signup and view all the answers

What is the highest temperature reached in the reaction involving NaOH?

44 degrees Celsius Signup and view all the answers

What role does the specific heat of the calorimeter play in the calculations?

It must be calculated separately and added into the heat equations. Signup and view all the answers

Calculate the heat absorbed by 100 g of water cooling from 32 degrees Celsius to 16 degrees Celsius using its specific heat.

-671 J Signup and view all the answers

What is the calculated value for Cs based on the calorimeter's experiment?

-16.28 J/g degrees Celsius Signup and view all the answers

Which equation properly represents the relationship between heat and temperature change in calorimetry?

Q = m imes Cs imes (t1 - t2) Signup and view all the answers

What materials' mass would you use for the calculation of the heat of fusion during the ice's melting?

Water and ice Signup and view all the answers

How is the heat of reaction for HCl and NaOH calculated in the second reaction?

(20g x 4.184 x (38 - 45)) Signup and view all the answers

Study Notes

Prayer Before Class

Holy Spirit, true source of light and wisdom, dissipate darkness and ignorance.
Grant a penetrating mind for understanding.
Grant a retentive memory and ease of learning.
Guide the work and bring it to success.
Ask through Jesus Christ, true God and true man.
Reign with the Father, forever and ever.

Post-Laboratory Discussion Experiment 5: Calorimetry

Topic: Chemistry for Engineers Laboratory
Focus: Calorimetry

Unit Intended Learning Outcome

Determine the amount of heat absorbed/released when a solid dissolves in water.
Determine and compare the amount of heat involved in 3 related reactions.

Calorimetry

Science of determining energy change in a system.
Measures heat released/absorbed during chemical reactions (heat transfer).
Cannot know the exact enthalpy (heat content) of reactants and products.

Calorimeter

Apparatus to measure heat flow in chemical/physical changes.
Measures quantity and direction of heat flow.
ΔH: change in enthalpy
- Negative for exothermic reactions; positive for endothermic reactions.

Two Main Types of Calorimeters

Bomb calorimeter: maintains constant volume.
Constant pressure calorimeter: maintains constant pressure (e.g., coffee cup calorimeter, volume changes possible).

Constant Pressure Calorimeter

Uses the First Law of Thermodynamics.
If heat is lost by the chemicals during reaction, it must be gained by the solution.
- q_substance = - q_solution
Enthalpy (H) accounts for heat flow at constant pressure.
- Heat absorbed/released = change in enthalpy (ΔH).
- q = ΔH (heat and enthalpy change are interchangeable).
Specific heat capacity: energy needed to raise the temperature of 1 gram of a substance by 1 degree Celsius.
To measure the enthalpy change for a reaction in aqueous solution, dissolve the reactants in known volumes of water.

Constant Pressure Calorimeter Procedure

Measure the initial temperature of each solution.
Mix the solutions in a foam cup.
Measure the final temperature.

Constant Pressure Calorimeter Calculation

Calculate the heat absorbed/released by surroundings (q_surr).
- q_surr = m × C × ΔT (mass, specific heat, change in temperature)
Heat absorbed/released by the surroundings is equal to but opposite in sign to the heat released/absorbed by the system (q_surr = -q_sys)
Enthalpy change for the reaction (ΔH) can be written as: q_sys = ΔH = -q_surr = - m × C × ΔT

Specific calculations: Examples

Given values for copper and water properties (mass, specific heat, initial/final temps) calculate the mass of water.
Given values for titanium and water properties (mass, specific heat, initial/final temps) calculate the specific heat of titanium

Activity Experiment 5: Calorimetry

Determine the heat capacity of the calorimeter.

Determination of the Heat Capacity of Calorimeter

Based on relationship: heat lost = heat gained
- Heat lost by water + heat lost by calorimeter = Heat gained by ice in melting + Heat gained by ice-water
- mwCp (t₁ - t₂) + Cs(t1-t2) =
- miHf + miCp(t2 - tice)
- (mass of water, specific heat, initial temp water, final temperature water, heat capacity, mass of ice, heat of fusion of ice, ice temperature )

Determination of the Heat of Reaction

Use the equation: ΔH_reaction = (mCp + Cs)(t1 - t2)
- Cp - specific heat of water (4.184 j/g-°C)
- m - mass of reactant(s)
- Cs- heat capacity of calorimeter
- t1 -initial temperature of water
- t2 -highest temperature after mixing

Examples of Reactions (Determination of Heat of Reaction)

Reaction 1(∆H₁)
Reaction 2(∆H₂)
Reaction 3(∆H₃)

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Description

This quiz focuses on the principles of calorimetry as part of the Chemistry for Engineers laboratory course. Test your understanding of calculating heat transfer during chemical reactions and the operation of calorimeters. Prepare to evaluate the thermal energy changes in various processes.

Chemistry for Engineers - Calorimetry

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