Ch.6 - Thermochemistry

Tro - Chemistry: A Molecular Approach 4th Edition

Tro4th EditionChemistry: A Molecular ApproachISBN: 9780134112831당신이 사용하는 게 아니라요?교과서 변경

Tro 4th Edition

Ch.6 - Thermochemistry

문제 101b

6장, 문제 101b

Use standard enthalpies of formation to calculate the standard change in enthalpy for the melting of ice. (The ΔH°_f for H₂O(s) is –291.8 kJ/mol.) Use this value to calculate the mass of ice required to cool 355 mL of a beverage from room temperature (25.0 °C) to 0.0 °C. Assume that the specific heat capacity and density of the beverage are the same as those of water.

검증된 단계별 안내

Identify the standard enthalpy of formation for water in its liquid state, ΔH °f (H2O(l)), which is typically -285.8 kJ/mol. This value is necessary to calculate the enthalpy change for the phase transition from solid to liquid.

Calculate the standard enthalpy change for the melting of ice using the formula: ΔH °melting = ΔH °f (H2O(l)) - ΔH °f (H2O(s)). This will give you the enthalpy change required to melt one mole of ice.

Determine the amount of heat required to cool the beverage from 25.0 °C to 0.0 °C using the formula: q = m × c × ΔT, where 'm' is the mass of the beverage, 'c' is the specific heat capacity of water (4.18 J/g°C), and 'ΔT' is the change in temperature.

Convert the volume of the beverage (355 mL) to mass, assuming the density of water is approximately 1.00 g/mL. This conversion is necessary because the specific heat capacity formula requires mass.

Calculate the mass of ice needed to absorb the heat removed from the beverage using the formula: mass of ice = q / ΔH °melting. This will give you the amount of ice required to cool the beverage to 0.0 °C.

비슷한 문제에 대한 검증된 영상 답변:

이 영상 해법은 위 문제에 도움이 된다고 튜터들이 추천한 것입니다.

주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Enthalpy of Formation

The standard enthalpy of formation (ΔH°f) is the change in enthalpy when one mole of a compound is formed from its elements in their standard states. It provides a reference point for calculating the enthalpy changes in chemical reactions. In this case, the ΔH°f for solid water (ice) is crucial for determining the energy required to melt ice into liquid water.

Specific Heat Capacity

Specific heat capacity is the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius. It is essential for calculating how much energy is needed to change the temperature of the beverage from 25.0 °C to 0.0 °C. Since the problem assumes the beverage has the same specific heat capacity as water, this simplifies the calculations.

Mass and Density Relationship

Density is defined as mass per unit volume and is crucial for converting between the volume of the beverage and its mass. Given that the density of water is approximately 1 g/mL, the mass of the beverage can be directly calculated from its volume (355 mL). This relationship is vital for determining how much ice is needed to absorb the heat from the beverage.

관련 실천

교과서 질문

If 50.0 mL of ethanol (density = 0.789 g/mL) initially at 7.0 °C is mixed with 50.0 mL of water (density = 1.0 g/mL) initially at 28.4 °C in an insulated beaker, and assuming that no heat is lost, what is the final temperature of the mixture?

Dry ice is solid carbon dioxide. Instead of melting, solid carbon dioxide sublimes according to the equation: CO₂(s) → CO₂(g) ◀ When carbon dioxide sublimes, the gaseous CO₂ is cold enough to cause water vapor in the air to condense, forming fog. When dry ice is added to warm water, heat from the water causes the dry ice to sublime more quickly. The evaporating carbon dioxide produces a dense fog often used to create special effects. In a simple dry ice fog machine, dry ice is added to warm water in a Styrofoam cooler. The dry ice produces fog until it evaporates away, or until the water gets too cold to sublime the dry ice quickly enough. Suppose that a small Styrofoam cooler holds 15.0 L of water heated to 85 °C. Use standard enthalpies of formation to calculate the change in enthalpy for dry ice sublimation, and calculate the mass of dry ice that should be added to the water so that the dry ice completely sublimes away when the water reaches 25 °C. Assume no heat loss to the surroundings. (The ΔH°_f for CO₂(s) is –427.4 kJ/mol.)

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교과서 질문

Use standard enthalpies of formation to calculate the standard change in enthalpy for the melting of ice. (The ΔH°_f for H₂O(s) is –291.8 kJ/mol.)

1855

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교과서 질문

A 25.5-g aluminum block is warmed to 65.4 °C and plunged into an insulated beaker containing 55.2 g water initially at 22.2 °C. The aluminum and the water are allowed to come to thermal equilibrium. Assuming that no heat is lost, what is the final temperature of the water and aluminum?

LP gas burns according to the exothermic reaction: C₃H₈(g) + 5 O₂(g) → 3 CO₂(g) + 4 H₂O(g) ΔH°_rxn = –2044 kJ What mass of LP gas is necessary to heat 1.5 L of water from room temperature (25.0 °C) to boiling (100.0 °C)? Assume that during heating, 15% of the heat emitted by the LP gas combustion goes to heat the water. The rest is lost as heat to the surroundings.

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