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Ch.7 - Thermochemistry
Chapter 7, Problem 50

How much heat is required to warm 2.50 kg of sand from 25.0 °C to 100.0 °C?

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Identify the formula to calculate the heat required: \( q = m \cdot c \cdot \Delta T \), where \( q \) is the heat energy, \( m \) is the mass, \( c \) is the specific heat capacity, and \( \Delta T \) is the change in temperature.
Determine the mass \( m \) of the sand, which is given as 2.50 kg.
Find the specific heat capacity \( c \) of sand. For sand, \( c \) is approximately 0.84 J/g°C. Convert this to J/kg°C by multiplying by 1000, resulting in 840 J/kg°C.
Calculate the change in temperature \( \Delta T \) by subtracting the initial temperature from the final temperature: \( \Delta T = 100.0 \text{ °C} - 25.0 \text{ °C} \).
Substitute the values into the formula: \( q = 2.50 \text{ kg} \times 840 \text{ J/kg°C} \times \Delta T \) to find the heat required.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Specific Heat Capacity

Specific heat capacity is the amount of heat required to raise the temperature of one kilogram of a substance by one degree Celsius. It is a material-specific property that varies between different substances. For sand, the specific heat capacity is approximately 0.84 J/g°C, which means it requires this amount of energy to increase its temperature.
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Heat Transfer Equation

The heat transfer equation, often expressed as Q = mcΔT, relates the heat energy (Q) absorbed or released by a substance to its mass (m), specific heat capacity (c), and the change in temperature (ΔT). In this equation, ΔT is calculated as the final temperature minus the initial temperature. This formula is essential for calculating the heat required to change the temperature of a substance.
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Units of Measurement

Understanding units of measurement is crucial in chemistry calculations. Heat is typically measured in joules (J) or calories, while mass is measured in kilograms (kg) or grams (g). When using the specific heat capacity in calculations, it is important to ensure that all units are consistent, particularly when converting between kilograms and grams or between Celsius and Kelvin.
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Units of Radiation Measurement
Related Practice
Textbook Question

We pack two identical coolers for a picnic, placing 24 12-ounce soft drinks and five pounds of ice in each. However, the drinks that we put into cooler A were refrigerated for several hours before they were packed in the cooler, while the drinks that we put into cooler B were at room temperature. When we open the two coolers three hours later, most of the ice in cooler A is still present, while nearly all of the ice in cooler B has melted. Explain this difference.

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Textbook Question

A kilogram of aluminum metal and a kilogram of water are each warmed to 75 °C and placed in two identical insulated containers. One hour later, the two containers are opened and the temperature of each substance is measured. The aluminum has cooled to 35 °C, while the water has cooled only to 66 °C. Explain this difference.

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Textbook Question

How much heat is required to warm 2.50 L of water from 25.0 °C to 100.0 °C? (Assume a density of 1.0 g/mL for the water.)

Textbook Question

Suppose that 25 g of each substance is initially at 27.0 °C. What is the final temperature of each substance upon absorbing 2.35 kJ of heat? c. aluminum

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Textbook Question

An unknown mass of each substance, initially at 23.0 °C, absorbs 1.95 × 103 J of heat. The final temperature is recorded. Find the mass of each substance.

a. Pyrex glass (Tf = 55.4°C)

b. sand (Tf = 62.1°C)

c. ethanol (Tf = 44.2°C)

d. water (Tf = 32.4°C)

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Textbook Question

How much work (in J) is required to expand the volume of a pump from 0.0 L to 2.5 L against an external pressure of 1.1 atm?

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